I would suggest a light meal between 4 & 5 p.m.!!
If you must stop and get something:
My number one recommendation!!
Subway: If you have one close by - get a salad or a 6" sub (watch the meat you choose and condiments; no mayo)! A lot of it depends on the plan that you are using. My choice is the salad! It's good for just about any plan as long as you watch what you put on it and the dressing! No crackers! (Plenty of veggies) If you get the tuna, be sure to make sure they don't put much or ask for it on the side (so you can limit it)!
A salad isn't great everyday, but you have many different varieties to choose from!
If there is no subway close by, choose a nice place that has a good salad or something that sorts your plan or can be customized by your order.
This will help, because you will have a meal before you get to class and what get as hungry! Plus it will keep you from eating a lot after you get home before you go to bed, since you don't get out of class until after 9 p.m.
If you determine that you will still need a snack during class many of the other suggestions that were previously given would work wonderful! Just be sure of your portions!