I have decided to get a little stricter with my...

I have decided to get a little stricter with my sons diet as he is always sick, not gaining weight and if he had the choice would live off biscuits alone! I have hidden the biscuits but I need some good ideas for healthy snacks. Especially ideas of easy snacks to take with us when we're out. I wonder if those le snack things with the crackers & cheese are healthy? Are there any prepackaged healthy snacks? (Other then fruit of course).