The vegetarian society would disagree with you, of course. Anyway, the simple way is to use some of your veggies to feed livestock, which subsequently feed you (and manure the ground so you can grow more veggies). I think it takes a couple of acres before a cow is feasable though, or two if you want year round milk.
A pig is more realistic, or if you have a reliable and cheap energy supply for the aerator pumps, a small trout farm tank doesn't take up much room.
Even less work is to shoot wild things that fly overhead.
Owain