In my class I allow the students to bring a small snack if they chose to have something quick mid-morning after our bathroom break. The snack should be something small that can be eaten within the five minute snack period.
Also students are allowed to bring water bottles that can be kept on their desk throughout the day if they get thirsty. If a child is found to be playing with the water bottles and they become a distraction, they may be asked not to bring them anymore.