A character or characters finds themselves adrift on the ocean without a means of getting to shore and little to no food or drinkable water. Usually, this is the result of a storm at sea, and if the characters in question are lucky they'll be in a lifeboat. If not they'll be floating on a piece of driftwood with nothing except the clothes on their back.
One or more of the characters may start hallucinating or acting crazy, or the survivors may start to argue over the remaining supplies while they wait to be rescued or manage to find land.
Often happens in stories about Wooden Ships and Iron Men.
Variant in De cape et de crocs: the heroes find themselves stranded in low water in the middle of the mediterranean sea, with nothing to eat or drink and no possible escape. One of them tries to fish, the other two start bikering and fighting.
Tintin: Tintin, Haddock and Szut are also lost at sea on a hastily made lifeboat in Coke en stock. When Tintin and Szut decide to drink sea water to stop suffering from thirst, Haddock mocks them... and promptly slips on the planks, falling head first in the sea and drinking more than both of them.
Open Water. Two scuba divers are accidentally left behind by their dive boat in the open ocean.
The sequel features a group of boaters who all decide to go swimming one day and then a series of increasingly improbable events keep them from getting back on board.
Parodied at the end of Road to Morocco, where Bing Crosby and Bob Hope's characters end up on a raft in the ocean. Following Hope's speech about certain death, it's revealed they're almost literally floating in the New York City harbor.
Actually happens, of all people, to Captain Aubrey of the Aubrey-Maturin saga. He has to rescue Dr. Maturin when the latter falls out of the Surprise's great cabin, but since the two are unable to grab onto the ship's boats, they are left to float and swim for a considerable period of time till they are picked up by a pahi boat piloted by some rather hostile lady islanders.
Slimer begins with the protagonists adrift in the freezing cold Atlantic in a life raft after their yacht sank.
The Island of Doctor Moreau also begins this way. In Edward Prendick's case, he's in the Pacific. He initially has a couple of fellow survivors with him, but they get into a fight after it's suggested they turn to cannibalism to survive. The two fall overboard and drown, leaving Prendick alone. Prendick is eventually picked up by a passing ship, but in the interim has gone nearly insane from sunstroke and lack of food.
Evoked by Ricky Gervais and Steve Merchant in The Ricky Gervais Show, when they asked Karl Pilkington who he'd rather save from a sinking ship. Most of Steve's argumentation was based on the fact that if Karl took Ricky on his lifeboat, he'd eat all the food in five minutes and let Karl starve.
The third-season Hawaii Five-0 episode, "Lana I Ka Moana" (whose title is Hawaiian for "Adrift") partially employs this trope when it starts with Danny and McGarrett getting their boat hijacked on a fishing trip, far enough offshore that it's no longer visible. The thief leaves them in the dinghy they found him in, which no longer has a working motor, and although it seems eminently possible they can save themselves (and eventually they do), at first Danny sees their situation as hopeless.
The subject of the Mr. Show sketch "Lifeboat" in which the raft passengers are members of a Jerry Springer-esque show. They're actually more concerned with their own problems than they are with finding dry land.
Horatio Hornblower: In "The Even Chance", it happened to Archie Kennedy. It was no accident. He had an epileptic fit during a covert raid and Hornblower had to clunk him unconscious, and his tormentor untied the boat he was in an attempt to murder him. The boat drifts away and he's lost and presumed dead. He appears again in "The Duchess and the Devil". The audience doesn't know much about the period when he was Lost at Sea as the focus is always on Hornblower.
Alluded to in The Legend of Zelda: Link's Awakening: Link gets caught in a storm and apparently washes up on a small island. By the end of the game he's defeated the Nightmares and caused a Dream Apocalypse, but he's still stranded in the middle of nowhere with nobody but a psychedelic whale and a couple of seagulls to keep him company.
One episode of The Simpsons had Homer, Bart, Ned, and Todd (or Rod) adrift at sea in a raft after a boy scout rafting trip goes awry. They are eventually saved when Homer is able to locate a Krusty Burger situated on an offshore drilling rig.
This is very much Truth in Television. One of the most well-known examples of the 20th century occurred after the USS Indianapolis was torpedoed in the Philippine sea in 1945. Out of 880 men that survived the ship sinking itself, only 317 ultimately survived the five-day ordeal.