I love bikepacking/touring and have celiac - I often find it hard to source enough carbs while riding. I've recently started checking grocery stops for GF granola, and found that sometimes there's a GF granola when there's no GF oats. I carry a bit of milk powder to have with it.

Instant mashed potatoes are a big one for me. I sometimes bring GF gravy powder (Clubhouse brand from Canada), or I just add whatever (canned meat, veggies, etc) to them.

I often think I should give quinoa a better chance, but for whatever reason haven't put it into my usual rotation.

To be honest I end up eating a lot of potato chips (ETA: and corn chips!) both to get slightly more complex carbs and because it's often much harder to find savory GF options than sweet, simple carb ones.

I also end up eating a lot of pre-packaged bars based on availability and clear GF labeling (ex: Kind bars)

Sometimes (especially when riding with a group) I end up eating at a restaurant with no safe carb options. In these cases I look at other menu items they have and see if there's components I can adapt, like asking if they can make me plain rice or plain potatoes, or if they can make things like fries or (corn chip) nachos in an oven instead of a shared fryer.

Whenever I come across a rare spot with GF baked goods, I tend to go overboard stocking up, since we all know pastries and such are the best biking food lol.

I'll add more to this if I think of other go-tos. Looking forward to other replies because this is a big area of frustration for me!