If I could go back in time to my childhood, knowing what I do now, I would cut out High Fructose Corn Syrup and refined sugars. Not just in my snacks, but in all meals. I would have been better focused in school and had more energy.
Having said that, here are a couple snacks I enjoy:
1) Fruits and veggies work as long as they are cut up ahead of time and put in small, sandwich-sized tupperware. This is so that when you open the fridge, you can grab it and start eating without going through the trouble of cutting it up. It has to be as convenient to grab as the bag of chips.
2) This takes more time, but a snack I like is taking pita bread or thin corn tortillias and putting some olive oil on them, and then put them in the broiler or toaster oven to make them paritally crispy. Tear those up into sections and use them to dip into a warm black bean dip.