DJB mentioned bringing panniers to Europe, I have carried two panniers onto the plane. One front pannier as the "personal item" and a rear pannier as my "carryon" bag. I do not want airline luggage handlers to crack my helmet in a checked bag, so I wear it onto the plane and then put it in the overhead bin above me. But different airlines have different rules for sizes. If my checked bag is approaching the weight limit, I try to carry heavy stuff in my carryon, etc. I always carry a luggage scale to make sure my checked bag is not overweight.

You did not say if you are carrying camping gear. Tent stakes or anything like that which a TSA agent might think is a weapon, that gets checked of course. Camp stove, I only fly with a butane stove now, too much hassle making my liquid fuel stove free of petroleum odor.
https://www.msrgear.com/blog/flying-...camping-stove/