Survivalist Stash

It's The End of the World as We Know It, or at least whatever small part of it the protagonist used to live in, and in the ensuing chaos our worn down, desperate and starving heroes stumble upon a Survivalist's Stash. It seems someone was Crazy Prepared enough to assemble a shelter, bunker, or some other refuge with all the essentials. Food, water, electricity, first aid, and good old guns!

The heroes will marvel at their good fortune, and lament the Irony that the person responsible for this gift died without being able to use it. Or are they?

Much like Goldilocks and the three bears, they may be trespassing into a very Crazy Survivalist's home without realizing it! Odds are even that they'll manage to defuse the following armed confrontation, though they may end up being chased out or having to kill the survivalist in self defense.

Examples of Survivalist Stash include:

Comic Books

Legion of Super-Heroes: During the second Universo story arc, the Legion has been outlawed and everyone on Earth turned against them by the mind-controlling villain. All their resources have been stripped away. Good thing they just happen to stumble across one of Lex Luthor's old hideaways, still fully stocked and functional after a thousand years.

Film

In Zombieland, the survivors find a Hummer stocked with automatic weapons.

Tallahassee: "Thank God for rednecks!"

The subterranean bomb shelter in The Road, stocked with food and high-quality booze.

Literature

Done in the Doctor Who New Adventures novel Sky Pirates!, when the heroes are stuck on an ice planet. Not a survivalists' bunker, though, but a stash left by arctic explorers.
The Road by Cormac Mccarthy. The creator of the bunker is dead.
Life As We Knew It
The heroes in Stephen King's Zombie Apocalypse novel Cell loot the home of the neighborhood gun-enthusiast for weapons and ammunition.
Prior to the Waterless Flood, the God's Gardeners in The Year of the Flood are encouraged to build and maintain "Ararats", basically food stores meant to enable them to survive the apocalypse. Given the nature of the Flood when it does come, the Ararats don't do most of the Gardeners much good.
In one part of World War Z, one of the survivors comes across a truck absolutely loaded down with canned food, weapons, and other survival gear. In a rather ironic twist, the driver did himself in, apparently from despair.
- She doesn't use any of it because she still had her military issued gear and since it's all civilian gear it would just weigh her down, and in a Zombie Apocalypse speed and mobility is everything.
in the Mistborn series, it turns out that Lord Ruler had made a number of these specifically in case of his defeat. They come in real useful when the shit hits the fan in the third book.
The Stockpiles in Deathlands are the US government's version of these; unfortunately there's no more United States left. Intrepid Merchant The Trader has become quite wealthy and powerful in this Scavenger World due to his ability to locate these hidden government stashes.
One way the protagonist of I Am Legend survives as long as he does is by finding stashes collected by other, failed survivors.

Live-Action TV

Battlestar Galactica has Helo and "Sharon" find a stash of food and anti-radiation meds in a cafe. Of course, it was probably planted by the Cylons.
Lost. Station 3 The Swan is stocked with food, an armory and various equipment.
The simulated-apocalypse Reality Show The Colony requires its participants to accumulate and defend the resources they need, creating an example of this trope for themselves.

Tabletop Games

The Morrow Project adventure Prime Base. The title installation has everything a Morrow Project team could want, if they can figure out how to make it operational.

Video Games

This is a frequent occurrence in the Fallout games, with the whole post apocalyptic scenario going on, it's no wonder.
Similarly, both Left 4 Dead games, since most levels begin and end in a saferoom stocked with guns, ammunition, and medical supplies. There's also one in The Sacrifice's comic.
In the Zombie Apocalypse game Rogue Survivor, you can put together your own Survivalist Stash! Of course, how long you can protect it (and yourself) from the undead, bikers, gangsters, starving looters, and all the other psychopathic jerkasses is another question...