To survive in MGS3, you'll need to eat. Pretty much any wildlife is edible, but their effects (and taste) vary.
Tastes great and recovers loads of stamina.
Recharges your batteries when you eat it. You can also throw it to use as a light source in dark areas, or throw it at Volgin to absorb his lightning attacks.
It's somewhat hard to get food from the large gators, considering that you can't capture them alive and that they fight back, but killing them will net you three servings of food. Each one tastes okay and gives you one whole bar of stamina. It's also great for feeding dogs and putting them to sleep.
Snake doesn't seem to like these much, but they recover one whole bar of stamina and never spoil. (It's also funny to feed them to EVA and listen to her reaction.) Oddly, the dogs will not eat these - they'll investigate it and sniff it for a bit, but they'll ignore it afterwards.
You can find these in enemy supply rooms. They taste great, never spoil, and recover two whole bars of stamina.
You can find these in supply rooms. EVA will give you a few as well at the top of the mountain overlooking Groznyj Grad. They taste just as good as Calorie Mates, and recover about the same amount of stamina. (Strangely, they're obviously of Japanese origin, but how they got into Russia is completely unknown, considering that Japan and the Soviet Union were never allied.)
Lay a mousetrap in Bolshaya Past South or Graniny Gorki South anywhere in these2 areas and wait about 10 minutes nearby. On your return, there should be a Tsuchinoko caught in the trap. Also, after receiving your equipment from EVA at the waterfall, it will be near a log in eastern Tikhogornyj if you caught it before. Tastes great, but don't eat it--finishing the game with it gets you the Infinity facepaint. which is useful for your next game