Yes, the restaurants are walkable as long as it's not 90 degrees with 90% humidity. While they are indeed all chain restaurants, I have found the Hooters and Chili's locations to be better than average for those chains.

Gas is running around $3 a gallon (haven't been to MCO recently to check on their prices in particular), so PaulMCO's advice is spot-on. The one or two gas stations closest to the airport are absolutely gouging tourists, and actually getting in trouble with the local authorities for their tiny signs. Drive a little further down Semoran Blvd and you'll find gas stations with much more reasonable prices.