adding to smackie's answer: there are no chairs reserved for people who order food. there are a few barstools by the upstairs bar, so if you get to the club early enough you might be able to grab one of those for the duration of the show. there are also stools in the VIP section if you happen to have access to that. you can order food at the upstairs bar and they'll bring it up to you (unless they've changed that service recently...)
every time i've ordered food from the Food Food window, it's been early enough in the evening that eating at the adjacent bar (while standing) hasn't been a problem. if it's really busy staph might ask you to make space for people ordering drinks.
suggestion: if you're going to a sold out show, get there on the early side if you intend to order food. showing up just before the headliner takes the stage and hoping to get food is a recipe for frustration: it'll be a challenge just getting to the FF window, and if they're still serving you won't have much space once you get your food...