I am the one who hands out the snack at school, so just make sure they can open it by themselves or it is pre-packaged. Bagels and cream cheese have been a hit in our class and I appreciate when it is already spread on. One mom popped popcorn, but packaged them individually so there was not a big mess trying to hand it out. My kiddos love the big pretzel rods, fruit roll ups, gummies, cut up watermelon, grapes (washed and cut into clusters really helps me out), boxed raisins and granola bars.
I also appreciate when there are a few more snacks than one per kid. I have had several times when someone tried to open something or fell down and it ended up in the wood chips and the child was left with nothing to eat. We save the snacks we can and if someone has forgotten it was their turn for snack we have extra for the day.