Broccoli, cauliflower, and bell peppers are all great, portable veggies that add crunch and filling. Eat a handful of broccoli, and it fills you up great!
I also have a go-to trail mix I use when I need a quick snack. A handful of this is so filling, and it tastes great.
Dark chocolate M&Ms
Large multi-colored raisins (the kind with the red, golden, and regular raisins in it)
lightly salted peanuts
lightly salted cashews
fresh shelled pecans (we live in Georgia)
Packs a serious protein punch, and even has a bit of sweet to tickle my taste buds. Feels like I'm being naughty, but it helps!