You can carry prist, but you need to fill out a hazmat form. We do it for 135 flights, but not too sure if you need the form for 91 or not. Wouldn't hurt just to CYA. We carry it in a metal tool box in the hell hole. (would not carry it in the cabin personally) It never hurts to have some if you fly in the islands. sometimes the prist injector breaks, and they you have to jump around to find some.