Well you don't want to make sheetz a restaurant. That would make it like everything else, like a Mcdonalds, Wendys, and things like that. You don't want to be a "wanna be." Be unique like you are already! Those fast food places have seating inside... Boring and unoriginal. Have more seating outside! You're majority of sales (i'd imagine, besides gas) are teenagers or college kids with their late night food cravings or lunch time. Personally, people won't go there day to day for a dinner like they would at McDonalds. Sheetz is unique like that. So this is what you should do. Have more seating outside so teens and college kids can have more space outside to BS and talk about nothing really. We need places to hangout and get away and nothing is better than a Midnight sheetz run with friends!! Nothing beats that, because it is UNIQUE.
Hope this helps,