Ramen noodles are my favorite inexpensive snack. When the water is hot, you can crack a couple eggs in it for the added protein. I also add frozen vegetables, and I can go ahead and stick the bag back in the freezer with a twist tie. As a vegetarian I do not add canned tuna, but the overnight manager at the grocery store where I buy my vegetables suggested it.

Chopped walnuts from the baking aisle are high in calories - and a good source of omega-3 fatty acids. I get raw, unsalted almonds there, too.