Flew from PHL to Jax this summer for Blue-Grey...carried on: Glove, jock, spikes, pants. Figured we could buy anything else if it got lost [yeah I know -- we could have bought a jock, but you know how some cups are...] Coming home, did the same, mainly b/c he had to pitch in a Legion playoff that night - almost didn't get the spikes on board; I think my FAA badge helped, but we had some close scrutiny!!
Catcher would want to bring anything that would fit - you can buy if you have to, but not lots of time to break stuff in - definitely take the mask and the glove. I know this is obvious, but don't even THINK about trying to take a bat - it's a little different with those guys that carry their guitar or fishing rods!