Hop on I-4 Westbound (exit is right off Central FL Parkway, at Westwood) and drive one exit up to state road 535. Or drive to the right of I-4 and take a left on Palm Parkway/Turkey Lake Road (same road, two different names), also to 535. You will find every affordable chain restaurant imaginable there.
There are a handful of restaurants by Sea World, but none I would recomend. OK, Flippers Pizza, behind Benngans and Steak and Ale on International Drive, is good. But that's about it.
For groceries, there is a relatively new Super Wal-Mart if you turn right onto Turkey Lake Road (see above), or a very nice Publix if you turn right out of Horizons, then right onto International Drive (by the 7-11). Wal-Mart should take no more than 5 or 6 minutes, Publix no more than 2.