Pick one of each for a full day of tummy trouble.
Breakfast
A's stomach isn't really awake yet but A doesnt have time to wait for breakfast.
The milk expires tomorrow so A eats as many bowled of cereal as it takes to use up all of the milk. (This could also work with eggs)
B makes breakfast for A. But A had way to much to drink the night before and isn't up for breakfast. Despite being super hungover they force themself to eat it anyway to make B shut up.
A just eats wayy too many waffles.
A eats a big breakfast before going on a morning jog.
A is hungover and tries to make themself food to cure it.
Lunch
A doesnt have much time between classes so they eat too much too fast.
A eats something at lunch that really disagrees with them. B rubs there tummy and gives them meds during their next class.
A's breakfast just isn't sitting right. Maybe eating a healthier lunch will help. But it just makes them painfully bloated.
A doesnt have much time between classes so they eat a big lunch and then go work out. Disaster ensues.
A is new to the school and their stomach isnt used to the cafeteria yet. B helps calm them down since they know the ropes.
Dinner
A ate too much throughout the day but has an important dinner to go to.
A orders a pizza bit has nobody to help them eat it.
A's dinner isn't sitting well. At an after school event their stomach keeps growling and B tries to discreetly help
A hasn't had a home cooked meal in so long that they way over indulge.
A drinks a few sodas with dinner to help them stay up to study. B ends up getting A to take a rest after a bad reaction to all of that carbonation