In case you've been in a hurry lately, here are some tips for navigating fast food as a glutard: Gluten Free Fast Food Options (via CeliAct)
I second their recommendation for Wendy's and In-N-Out. Wendy's even has a list of gluten free offerings -- looks better that it is, though, because they include condiments and sodas. I tend to choose Wendy's over others because they went through the effort of making a list. ...Reinforce the behavior you want to see. Wendy's staff has also generally been able to answer my questions accurately and often have dedicated fryers for fries. I mean, what's the point of fast food if you can't eat the fries??? I'm jealous of anyone who lives in In-N-Out territory. Their food is simple so you don't have to worry too much about a bunch of crappy additives. I always hit them up as a fast food treat whenever I am in range.
I second CeliAct's advice to stay away from Taco Bell. T-Bell is a ginormous disappointment for glutards. Spoiler alert: their "meat" contains a substantial amount of fillers, including oats. In addition, I haven't had any luck at Burger King (who is inferior to Wendy's in every way anyway).
I want to add Chipotle to CeliAct's list of good options. Like Wendy's they also have a super clear allergen list. Plus, you can eat ALMOST anything here as a glutard. Just no flour tortillas. Chipotle has been so good to me (unlike Qdoba, which I have had varying luck with)!
Wherever you end up going on the run, be sure to check any available allergen info available (it can change regularly) and don't be afraid to make requests to avoid cross-contamination.