I think part of it is dreading being poked, prodded, examined, stared at, searched, x-rayed, and otherwise intruded upon as part of my cross-country journey. I hate that feeling of trying my best to comply with the rules, but not really knowing what they are... Worrying about my choice of reading material, for example. Making sure I don't have anything even vaguely weaponlike on or about me. Should I leave my nice fountain pen at home, in case they get anal and start confiscating? It's pretty pointy looking, you could put an eye out with it if you were truly determined to.
Of course, the frustrating thing is I could put an eye out with damn near anything if I had to, in a pinch - up to and including my bare fingers. So why should I have to be concerned that my writing utensils are going to be taken?
I guess what the issue really is concerns how this plays into my general position on the continuum of normal to freak. I wasn't very good at being normal even when I was trying to pretend - not just trying, but working Really Hard at it on a daily basis. That was years ago, anyhow. I'm woefully out of practice at this late date. So I feel like I'm constantly moments away from being apprehended for sheer alienness...
Then there's the tie in to the Big Menace theory of the universe. I was raised to believe that the world in general was a Bad Place, if not wicked or downright deliberately Evil. This has had the side affect over the years of imparting an aura of menace to the sorts of proceedings that "everybody" is familiar with but with which I feel less than familiar or comfortable. Plane trips are certainly part of standard North American culture for my social and economic cohort, but personally I can still count the number of times I've flown somewhere without resorting to my feet. So it's still not really run-of-the-mill. It's the perfect level of not-quite-familiarity to allow doubt and disorder to creep into the proceedings.
Bah. I'm sure everything will go fine.