Canned food and bottled drinks
Food and non-dairy drinks preserved in cans and bottles and found in dumpsters by dumpster diving are generally all very safe to eat and drink, just wash the cans/bottles and keep them cool. Most of the time there is nothing wrong with them except the label went off or something got spilled over.
As long as the can remains sealed tight, canned food can last almost forever. Just make sure though, that any canned items are absolutely sealed, or they may be bad. Swelling is also a sign of something being off, so leave badly swollen cans behind. It is also good practice to smell the contents after opening the can and if it smells fine, it is fine.