Ichigo snorted, "I have a silver cross and several rolls of duct tape under my bed, a box in a location only I know about in case an Ichigo Kurosaki from the future deems sending me a message necessary, I carry picklocks in all of my shoes, I secretly own a car I keep parked on the other side of town, I had Kisuke make fake European passports for the both of us, I own a condo in Tokyo that I bought while disguised as a foreign woman by the name of 'Falsa', I bought the warehouse my sister's bodyguards use as base so that I could legally build a separate room large enough to fit a Gundam, just in case I do get a Gundam."
Xander in Working for the Weekend is teleported once a week to an Earth with no humans and since it always happens at the same time, he makes sure to prepare. Not only does he carry numerous weapons (machete, pepper spray, and air horns among them), enough food for a few days, and containers to take any eggs or seeds he finds (on behalf of the Mayor), but he also brings enough of everything for two people just in case someone tags along. Buffy wondered why he dressed like a lumberjack in winter when they ended up on a tropical island, which Xander explains as he never knows where on Earth he'll land so he dresses for freezing cold but includes cooler clothes. He even brings a Bag of Holding supplied by the Mayor.
The IDSE appears to be this in Kyon: Big Damn Hero, preparing tools for interactions with places that may not exist in case they do and any of the tools, such as a Dimensional Anchor, are necessary.
In A Tale Of Two Rust Buckets, the Colonial Fleet is stated to have contingency plans for numerous situations, including such things as the return of the Lords of Kobol, or a revolt by the Junior Pyramid League. Adama implements their first contact plan when he encounters Destiny.
In The Rift Effect (part of the The Omniverse Event) Bernice Summerfield has a way to basically come back from the brink of death - mainly because her friends had become so savvy to the fact that she nearly dies, wherever she goes.
This trope, more than anything, is why Jadeite's attempt on Nanoha's life failed in White Devil of the Moon. Everyone at the wedding who could fight came armed and prepared to do so, just in case. Justified if you've seen Triangle Heart 3 because you knowwhat happened the last time the Takamachi family had a get-together.
In Nothing Wrong with your TV, Alex (a post HeelFace TurnControl Freak) keeps two backups of his remote as well as two single use remotes that will take him to a universe where he can build a fully functional version and a set of tools to jury rig a remote, just in case he's stranded somewhere without his regular remote. Unfortunately for Alex, Spike rifled through his belongings and ate the lot.
The protagonist in Dragon Age: The Crown of Thorns managed to get everyone of the main cast out of Ostagar alive, along with the treaties, because he prepared for the possibility of Loghain not charging when he was supposed to. Granted, he'd had a discussion with the man earlier, when they both traded deep observations of one another. And this is just one of the many examples.
Harry Potter and the Methods of Rationality depicts Harry as (trying to be) one. The brief appearance of Mad-Eye Moody manages to upgrade his canon use of this trope. Apparently that magic eye of his that he has constantly scanning in every direction doesn't actually need to move—it provides perfect 360 degree vision no matter where it's pointed. He moves it around so that people think he needs to.
Also, the aurors have a code (RJ-L20) for "a prisoner is attempting psychological warfare and succeeding". The protocol for that code is to relieve the auror who calls it in and ask questions later.
In Oh God Not Again!, when Pettigrew is caught, Luna pulls out a animagus-proof jar that her father had her carry around in case she ever ran across an illegal animagus she wanted to capture. Even Harry is surprised by this.
Delenda Est: Harry never apparates directly to his destination. He apparates to half a dozen locations first. And that's if he doesn't think he's actively being followed. When Voldemort follows him, Harry apparates several times, running several yards before apparating again. When Voldemort still catches up to him, he uses fiendfyre as a distraction, apparates a few dozen times all over the area before apparating away, portkeying to another location, apparating directly over the ocean and waiting until he almost hits the water before apparating to his actual destination. He also has over a dozen safe-boxes filled with spare wands, potions, and multiple destination portkeys hidden throughout Great Britain.
Sean Moon: Case B scenarios are those where the majority of the House is in the Great Hall or class or otherwise out of the dorms. Class 5 scenarios involve a major threat to the school. German suggests that the threat is physical destruction or demolition. Evacuation Beta-funf requires us to get you all out of the school, and the seventh-year prefects are to go and lock down the potions labs and dorms so that the damage is minimalized.
Harry: If you were a Ravenclaw you would know all of this but you would probably only bring the most common documents. Only a Slytherin would see the benefit of bringing the most random forms just on the off chance that someone would need it. They like the shock of being prepared and outsmarting everyone in the room.
In Harry Potter and the Quantum Leap Hermione thinks of 151 things which could go wrong with transporting Norbert the baby dragon to the top of the Astronomy Tower and comes up with an appropriate plan for each and every one.
In A Second Chance at Happiness? Maybe? Charlus preserved some of his late first wife's blood on the off-chance that he might someday have to blood-adopt a bastard child to make it look like they were born legitimately.
A lesser known pureblood house of Morgan were survival nuts who conducted illegal experiments to make sure they had a contingency plan in any emergency. They had documented and conducted as many what if scenarios as possible over the years to ensure that they were prepared for anything. Most of the experiments were dangerous.
In The Price is Right Harry decides to carry his miniaturized school trunk around with him at all times.
What if there was a fire? Some inexplicable fire caused by unknown magic or someone in the room spontaneously combusting, and everything was destroyed? What if random kidnappers of remarkably prodigious skill broke into the school and dragged him away in a potato sack just like in those movies? What if he fell in a puddle and needed a change of trousers? He heard that the Potions professor liked to give detentions where they scrubbed out cauldrons, what if he needed his rubber gloves and face mask? Some of the portraits looked rather lonely, what if he ended up deciding to play a game with them? He'd need his playing cards and board games in that case. Really, it was only good sense that he bring everything with him.
In Endless Summer Days, the Global Justice Network (along with numerous other agencies around the world) have that they call the "Crazy Eight": plans for scenarios they think will never come up, including time travel. When Ron seems to be in a "Groundhog Day" Loop, having remembered the entirety of the current day's events, they first test him for psychic potential then activate the code for time travel, which automatically deactivates the moment it's activated, making it only useful for time travelers.
In Progress, the Cake family is insured against acts of goddesses. Which comes in handy when Pinkie Pie accidentally freaks out Princess Luna, and she trashes part of the place. They live with Pinkie Pie, getting an extremely comprehensive insurance policy probably seems like a sensible precaution. Of course, 'extremely comprehensive' policies may not cover against 'Acts of Goddesses'...
In Whispers, Moonthistle carries a saddlebag packed with a random assortment of tools that she might need someday ("I made a list.")
One of Moodbeam's friends had only one weakness: Nutella, which Amber Night just happened to have. You know, just in case.
It also just so happened that she recorded her entire quest to recover her Pop Tarts. She then proceeded to use the film as blackmail to get the princesses to give her back the Pop Tarts. It didn't work, but by selling it, she did apparently make enough bits to buy Canterlot Castle.
Way back when she first took Trixie on as a student, Luna put a tracking charm on her, just in case, and never actually undid it, again just in case. It comes in handy when Trixie disappears entirely, due to a case of accidental reality-hopping (long story).
Before he was sealed away in Tartarus, Tirek left fragments and copies of his soul scattered about the place, with the intention they'd one day absorb enough negative emotions to become their own individuals. Luna and Celestia thought they'd gotten all of them, but as it turns out, they missed a few... One of which turns out to have been hidden almost under Luna's nose, right on the edge of the Everfree Forest itself.
Sunsplit Saga: In Sunsplit, Twilight Sparkle, who has more than one backup quill, she has "an array of colorful feathers from her saddlebags", along with a "ballpoint pen", that she only brought out, because all her quills were gone, and won't burn up like her quills did.
In Marked for Death, being crazy-prepared is how your group of missing-nins survive and win. Planning with multiple contingencies is highly encouraged, although sometime the planning doesn't always account for everything. When that happens, shits hit the fan as in Chapter 65, in which the players didn't account for the opposing jonin to be awake, forcing them into a mortal battle before the team run away, only to be chased by Hot Spring and Leaf nins when the rolls just didn't work out..
Shinji And Warhammer 40 K: Emperor Shinji knows what you're planning even before he's met you. He also knows the odds of anything (whatsoever) occurring that could potentially derail his saving of humanity, and has already prepared at least four different methods, each, to deal with it. In fact, the only thing he doesn't know is... why him?
Mr and Mrs Gold: While Rose/Belle was interested in Rumpelstiltskins dagger, she took precautions and made sure to have countless replica daggers hidden all over Storybrooke and the Enchanted Forest. Some of them arent even spelled right.
In This Bites!, Mr. 3, when he catches up to Cross and Soundbite in Rainbase, has learned from his experience with Soundbite's powers, so he came prepared: breath control to keep him from hearing his breath, a wax vest to mask his heartbeat, and earplugs to guard against Soundbite's distractions. The Unluckies, Ohm, and the Foxy Pirates are among others who used forewarning to guard against Soundbite's powers.
Cross manages to be this to a lesser extent due to knowing most of the plot up to Dressrosa, such as saving most of the gold they got from Skypiea to both repair/save Merry and purchase Keimi.
In Episode 67 of Sonic X: Dark Chaos, Beelzebub put a shield over himself in case Tails tried to attack him, planted a self destruct mechanism in his lair in case Sonic and friends tried to free the slaves there, and installed an escape pod - complete with Warp drive and communications - in his chamber in case Sonic and his friends attacked him directly and he was forced to flee.
Maledict doesn't pull any punches in the Episode 75 rewrite either. He puts a Warpspace jamming field to prevent the heroes from fleeing and summons the Galaxy Crusher to take the entire Milky Way Galaxy hostage and bully Sonic into submission. He also was prepared to change his master plan if something failed - when Tsali betrayed him, Maledict shut his body down with a reset phrase he programmed into Tsali years before. He also knew exactly where the Metarex were if needed, in case his pawns ever found out the true identity of his "M" alter ego.
Alpha from Clash of the Elements is a deconstruction of this trope. He is so prepared for every possible scenario, including the possibility that everyone he knows on the planet could one day become corrupted or be forced to reveal information to the enemy that he has been consumed by a feeling of paranoia that has left him unable to trust let alone form a bond with the people that stick around him, save for Mario that is.
In Worldwar: War of Equals, once the aliens are confirmed to be a threat, most of the world stocks up on weapons, beef up their militaries, research anti satellite weapons, and even restart some previously canceled weapons projects all to combat the incoming invaders.
With This Ring: Batman takes the cake. He managed to take down Constantine, when John was under a spell that made him invisible and so that no one wanted to even look at him. Batman noticed that no one was going into a certain part of the room or even looking at that part of the room, so he started attacking it to make sure.
The Russian Research facility in regards to speedsters. They have cameras that can record at high-speed, shrapnel mines designed to kill and corral speedsters, gas dispensers, walls made of different materials with differing densities and a high-voltage current so you can't just vibrate through them, and a nuclear self-destruct device, just in case.