If you were to portion out a snack ahead of time, would that help? I count out grapes and put them into ~100 calorie baggies right when I bring them home from the store. I also like making snack bags with turkey pepperoni and low fat cheese cubes - turkey pepperoni has SO fewer calories than regular!
I like "poppable" stuff for when I'm reading, watching TV, internet surfing...
Also, if it would help having a large volume of something, maybe try popping your own popcorn? Not only is it healthier, it's CHEAPER! 3 cups of air popped popcorn is going to put you a smidgen under 100 calories. I put the kernels in a brown bag and throw them in the microwave for a minute and a half to two minutes -- no oil required. I like to spray it with I can't believe it's not butter spray and a shake of popcorn seasoning -- white cheddar is my favorite at the moment.
I struggle so hard with night time snacking too, I had 300+ calories of animal crackers just last night since I wasn't paying attention.
We can do this!