You seem to be young (I am too!) so hopefully I can help ..

These are my favorite snacks!
- Quaker rice cake (Salt free) with 1 tbsp peanut butter (reduced fat) - about 130 calories.

- Baby carrots with 1 tbsp Kraft Free Ranch - about 80 calories.

- Quaker rice cake - any flavor! They vary but usually aren't more than 60 calories.

- Quaker quakes - any flavor! Usually aren't more than 60 or so calories.

- Fat free, sugar free Jello with fat free Cool Whip - I make my own little single servings (it's cheap!) by putting the Jello into small, round Glad containers before it sets. Then I top it with whipped cream! I also do this with fat free Jello chocolate pudding. These are about 100 calories, if not less! The Jell-O is probably about 30 or 40.

- Dannon Activia yogurt - about 90 calories, I think? So good!

- Breakstone's Cottage Doubles - These are more of a meal for me but if you're really hungry it will do well! They are about 130 calories and are lof in fat.

- Kellog's Special K Bites - The Chocolatey Crunch ones are amazing! 90 Calories!

I hope I helped!!!

You don't have many calories to work with on non workout days, so I'm assuming you want snacks in the 100 caloriesh range.
There are a lot of great Fiber bars with about 100 calories, they even have ones with mini chocolate chips, dried fruit, butterscotch chips, etc. for about 110-120 calories (Fiber One bars are my personal favorite).
You can also make sandwich for about 100 calories, lots of more natural breads are filled with fiber and have about 40 calories in them, with a couple thin slices of deli meat and mustard it will come out to be about 100-110. You can also add lettuce, tomato, and onion and barely add any calories.
I also just LOVE cheese, so I know how difficult that can be. I love to mix either feta or goat cheese with egg whites and add hot peppers, and these can be made at about 60-100 calories, depending how much egg whites/cheese you use. I also like to have fresh mozzarella with a few cherry tomatoes and sprinkled with balsamic vinegar, about 100 calories.
An obvious answer is the 100 calorie snack packs, they offer everything from goldfish to mini cookies now.

I like cottage cheese with an apple or triscuits. or prunes and a banana and hard boiled egg. (I try and eat protein with my carbs)

thanks for all the great advice everyone! y'all are making me hungry!