Wendy's

Wendy's has one of the most extensive GF menus of any fast food restaurant.  The list includes baked potatoes, chili, salads, and burgers or grilled chicken sandwiches (minus the bun).  The Frosty is also GF, which is great news.  The fries themselves do not contain gluten, but may be fried with other items in the fryer.  The baked potato is a better option anyways.  I have uploaded a picture of the sour cream and chive baked potato and the chocolate frosty.

They have many locations around San Antonio, so you can search for the closest one on their website.