The best thing you can do for our furry (or scaly or feathery) friends is to not eat them!!!! I know it may sound hard, but a vegetarian or vegan diet is not as hard as it sounds. I am a vegetarian, and my diet consists of a lot more than sticks and leaves! There are tons of fake meats like "not dogs" and "wheat meat". I personally have only tried soy milk!!! I eat lots of pasta, fruits, and veggies. Here are a list of some things that are vegetarian that do not require a trip to Whole Foods:
Spaghetti noodles and meat- free Ragu sauce
Macaroni and Cheese (unless you don't drink milk or eat butter)
Veggies and Dip
Fruit with peanut butter
Bean Burritos (my staple)
I am sure that you eat some of this already.