For Eastern Europe games
this page is pretty useful. I would think the Granit-style bunker would be the sort characters in Poland would find. I'd assume that if they weren't destroyed early in the war their warheads/PELs would have been removed but then be reused for supply caches. While the pictures show the bunkers without doors, originally they had heavy blast resistant doors on either end of the tunnel. They were also hidden in forests and out of the way places. In the aftermath of TDM they could easily get lost and/or be left undiscovered until the PCs find them.
Storage bunkers in the US are going to be similar, half-tubes with a rectangular plan and a heavy door on at least one end. Then covered over with a bit of earth so it looks like just a mound from a distance. The width and height should be enough to fit at least one tractor and trailer. Inside might be trailer vans, ISO containers, or just shelves and pallets.
As for content possibilities:
- Pallet of ammo boxes (5.56 N, 7.62 S, or whatever region appropriate)
- Pallet of freeze dried food (camping food) in a variety of options. Package dates are all pre-TDM.
- Business band radios with cases of spare batteries.
- Several cases of canned vegetables and fruits. The cans are in good shape and all the seals are intact.
- Boxes of civilian outdoor clothes including boots, socks, and winter parkas.
- Several 1000 liter tanks of clean water.
- A pallet of mixed trade items (cigarettes, candy, liquor).
- Several boxes of code books, maps, and other useful Intel on the major OPFOR.
- Coded documents and maps leading to something (other caches?!?)