Shoot i just typed up a long response and lost it

Anyway, if you are taking Cam's carseat please please please DO NOT check it with your luggage unless you are going to pack it all up in a box with padding int he box and stuff. It is extremely unsafe to use a carseat that is checked with luggage because the machines will beat the crap out of that thing (yes, even if its marked fragile, dh used to work in an airport) and its possible the seat could be damaged. The thing with that is that you wouldnt necessarily be able to tell the seat is damaged unless you got in an accident and the seat failed for some reason... it could still be damaged even if it doesnt have a huge crack down the side. If you arent going to use his carseat on board then please at least carry it with you to the gate and gate check it, that stuff is at least hand loaded onto the plane so its a tad better. And btw, i think you're so brave for not getting him a seat (though i totally understand with the cost), we could barely keep M contained for the few minutes we let him out of his seat when we flew back in March and he wasnt even walking yet then!
Otherwise the only tip i can think of is if he's going to be sleeping in a pack and play maybe you cold practice a few days ahead of time? and even if you dont think he's attached to anything i'de still bring something like a blanket that is unwashed. Also, take a blanket with you on the plane ours got surprisingly cold! Otherwise just make sure you take snacks and a new toy or something that he'll be interested in. He might also have trouble with his ears popping so if you think that might be a problem (it wasnt for M) try to have him drinking or eating something he really has to chew like a giant marshmallow during take off and landing. You could also give him tylenol. I agree with comfy clothes and if he's going to be riding in a stroller to the gate i'de just skip putting shoes on him also, one less thing to worry about taking off at the gate.