Snacking is important fuel for me. I look for snacks higher in protein as they keep my metabolism burning and help reduce sugar cravings -- plus I find they satisfy me longer than a sugary or higher fat snack.
nonfat Greek yogurt is my favorite --
comes in two 32 oz containers at a great deal
when compared to the grocery store.
I love it and it makes great smoothies, too.
Speaking of nuts -- a few almonds are always in a baggie in my purse or the car.
A hard boiled egg is one of my favorites for "on the go" - high in protein, low cal and low fat. When I was a full time student, I took two already peeled along with a piece of fruit for lunch between classes. I will also grab a roasted, skinless chicken breast in a hurry.
I also keep a stash of protein bars on hand as more of a meal replacement than a snack if needed. They've gotten much better over the years. Some favorites are by Pure Protein, Balance (love the lemon meringue), Zone and Target's Market Place brand. Most are 170-210 calories with 12-20 grams of protein.
Obviously, this is not a complete list -- just a few of my favorites. I hope it gives you an idea that works for you.