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.
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.
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.
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?
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.