With me, it's any kind of travel papers/passes. When I lived/worked in Minneapolis, I commuted by bus and my employer provided a monthly unlimited bus pass.
I loved riding the bus, but became obsessed about losing the pass. I'd get it out of my wallet and put it in my front pocket...then I'd stick my hand in my front pocket and check it. Then I'd take it out and look at it, to make sure it was the pass and not something else, then I'd stick it back in my pocket. Then I'd put my hand in my pocket...over and over for the 45-minute ride home.
I took to making sure I always had about three times the bus fare in cash in case the 147th time I checked for my pass, it magically turned into a library card, so I wouldn't be thrown into bus prison for hopping the bus without the fare.
It's half the reason I'm pure hell to travel with - I spend the entire time obsessing over my boarding pass, my passport, my driver's license, my landing card, any kind of travel documents, I constantly check, recheck, and re-recheck, and as I pass through each step of a journey, I worry over not being allowed through the next checkpoint, because of my documentation being wrong.
A large part of that (self-analysis continues) is that I absolutely am terrified of holding up a line. I've gotten mild panic attacks when I've been in a line and it gets to me, and I have to fumble through my papers. The whole time, I'm worried everyone behind me is noticing that I'm the jerk screwing up everyone else's day because I handed over my credit card instead of my passport and now oh god this guy probably thinks I'm trying to bribe him or something and as soon as he plays along and let's me through he's pressing that secret button under his little podium that they all have to silently summon security and they're gonna drag me to a room and beat me and stick a flashlight up my butt looking for drugs!!!...and that's when I get so worked up, I drop all my travel docs all over the floor in front of the agent and by then, I really just want to go back to the house and forget the whole thing.
I hear you. I am not afraid of flying -- my best friend is terrified of flying. I get anxious about some of the same things you do. In the past, I always tried to be to the airport early, and sit at a bar near my gate, and drink. Self medication. Not sure what I'll do, now.
I pretty much fly through the TSA checkpoint. I have the whole routine down. Three tubs -- one for my camera bodies, one for my MacBook, and one for personal items. I wear slip-on shoes (usually Berkies), and comfortable athletic pants with a drawstring, no belt. (I don't like to wear a belt when I'm working, either -- belt buckles and concours quality paint jobs are not friends). I can unpack, go through the scanner booth, and pack up in a flash.
By the way, I did a plane to plane photoshoot around Dallas, and the aircraft company took us to this BBQ joint at a small airport in the middle of nowhere. On the way back, I sat in the co-pilot seat, and the pilot let my fly the plane -- we had a "safe-word" that meant, "let go of the controls, the pilot is taking control." I was not one bit anxious. I loved it. Same with cars. I am completely at ease at 150 mph. I guess the stimuli coming from the experiences take over.