An ultramarathoner friend of mine has one of those. Yeah, not sure how that would work going through TSA. Hey, it's not a liquid!! (yet...)

Exit row window seat is always a little chilly. I'd go for that. The main time I'm hot on an airplane is at boarding time if the aircraft has been sitting there for a while. At airports used to dealing with hot weather, they're usually good about closing window shades while the aircraft sits. But not always...sometimes I'm sitting there sweating and mentally counting the seconds until they fire up the APU and get some air moving through the vents.