Tuna and Crackers!
Easy as can be, good source of protein, crackers provide a nice crunch, and the snack is very filling.
To make the tuna, I just use whatever is cheapest, and I buy the ones that are in water, not oil or anything else. Then I mix in light Mayo (have you tried the canola mayo yet, it is supposed to be super yummy, and lighter than the real stuff), diced celery, and relish. You can use whatever crackers you have on hand. I like the Rice crackers. They are thin, crunchy, and lightly salted. You also get a ton of them per serving, so your hankering for a salty snack is sure to be filled without over-doing it!