Hi Genevieve!
I understand your concern. We've ordered the Deluxe Dining Plan in previous years and found ourselves..as they say.."biting off more than we can chew!" :-)
The Deluxe Dining is a TON of eating, so be ready...
Yes, there are some quick service restaurants that will allow you to convert 1 meal credit into 3 snacks. I say "some" because not all of them do this. There is no official list, so if you're considering converting (or I like to say downgrading), you just have to ask the quick service folks inside the restaurant first before making your purchase.
There are 3 quick services we were able to do this: The food court at Pop Century, Contempo Cafe' at Contemporary, and Pepper Market at Coronado (which, I believe, will no longer be on the Dining Plan as of 2011).
So, for participating restaurants, 1 meal converts to 3 snacks.
Have a good time enjoying all the good food!