This guy is correct about trapping being better than hunting. If you've got plenty of squirrels, get a 10 foot length of 6 or 8 inch PVC pipe and cut it into 3 or 4 lengths, capping one end of each length. Smear a lil oil on the insides, plant some peanut butter at the bottom, afix it firmly to a tree, and check back once a day on each one. If squirrels are abundant where you live, then you should be able to to pull at least 1 squirrel a day with a set of 3 or 4 traps like this.
NOTE: this method of squirrel trapping isnt legal everywhere (it's not legal where I live), but if society gets to the point where you need to catch squirrels to live, then it won't really matter, so it doesn't hurt to keep a couple pipe lengths and a jar of peanut butter in the closet.
Also invest in one or two live cage traps, and some cat food to bait them with. If you need meat, it will catch you possum, raccoon, and even stray cats if you're hungry enough to eat those.
Trapping requires WAY less calorie expenditure than hunting does, and so in a situation where you're fighting starvation it is 100% the way to go.