Hi, Jane! There are a ton of snack options while on the Disney Dining Plan. You'll find snack options at some of the carts, in some of the shops, even in the hotel food courts.
If you visit this site
Disney Dining Plan, you'll get a list of all the participating locations and an idea of what some of the snack options are. It varies by location, but you can get popcorn, fresh fruit, ice cream, muffins, cookies, individual sized bags of chips, an egg roll, and even the famous Dole Whip.
There are sites like disboards.com that actually keep track of what other guests have used their snack options for. You can do a Google search or go right to the site and do a search to see the extensive list of things that have qualified as a snack.
I hope this helps!