We thought Hurricane Hanna's (the grill outside near Stormalong Bay) had a nice quick service menu, and the Beach Club Marketplace has a quick service menu, too. The Boardwalk Pizza Window is another possibility, and I've heard other posters mention options at Swan/Dolphin. Boardwalk Bakery is another option, as previous poster mentioned. And if you are looking for quick and casual, Beaches and Cream is a good choice - but it's table service.
One of our favorite things about BC is that we are literally right next door to World Showcase in EPCOT, and we eat there as much as we can (4 out of 6 nights for our next trip!) So if you have park hoppers, you would also have access to any of the quick service locations in World Showcase.
P.S. Debbie B. has a great point (below) about the dining plan. It's been a while since we've done the dining plan, so these are just the options we are aware of from recent non-dining plan experience!