The best things I have found
-Any protein bars (I personally take Zone Perfect, low in calories but 12-14g protein)
-Precooked chicken/steak, heat it up in the microwave at work/school
-Greek Yogurt, high in protein, only about a buck per container, low calories
Just remember, unless you just worked out, your body can only digest about 30g of protein at one time, so keep track and don't waste your money on putting too much protein in your body cant use.