Travelling for me is somewhat akin to shooting stress into my eyeballs, minor part going from point A to point B and major part stress management; it wasn't until a couple of years ago that I experienced the joy of travelling as an experience rather than a means to an end, but that's an aside. There is a definite period - dependent on the type of journey - where my stress is maximised and occupies a space somewhere between short-term "let's go over here!" and long-term "right so I need to be at this place at this time". That zone is where I don't have enough time to prepare and more than enough time to fret and obsess. The long term planning allows me to purchase things that make me feel like I'm prepared and most importantly of all, plan for ifs.
My brain mostly works on the idea of "if". Given time to gestate, certainties and decisions are questioned and scrutinised; for instance, on a journey to London for a meeting at 1:30pm I know the train I should be catching but if something happens with that train, I can catch another one however many minutes later. Having multiple ifs is when I'm most relaxed, and mostly they come from doing the journey before or planning for it or having as few immovable times and places as possible. This mentality usually translates to showing up at whatever transport station is the most important in the journey (train stations and airports fall into this category) with "ample" time to spare. Ample time usually equating to three or four times longer than I really have to wait: the more time I'm sitting twiddling my thumbs is more time that could have been used up on ifs.
For a long time, I scoffed at document wallets; the ones touted in shops of sundry right next to the "luxury passport holder" and neck pillow (ensuring you get the minimum amount of sleep for maximum amount of neck discomfort). I then realised that document wallets serve the purpose of compartmentalising items which in turn compartmentalises the part of my brain worried about the location of all items on my person at all times, thus reducing my worry. I could, as an example, just fling everything into a backpack and extract items and documents as and when I needed them; however, my backpack also contains a magazine and food, I'll have to navigate them (sacrificing precious seconds) to get at just one item. Conversely, keeping everything together potentially makes it easier to pilfer, unfortunately thievery is a game stopper and one has to balance the mental anguish of keeping items safe with alleviating angst. I still scoff at single passport covers however because they serve no other purpose than to kill a cow (another cow potentially if your passport is already leather bound) for your style or to satisfy your lust to "bling" your travel documents.
I have, if anything, mellowed out somewhat from my earlier days of borderline neuroses. This has mostly come about due to further journeys and understanding how systems work (where to go in an airport, where to look for times, where best to sit and people watch) but mostly by travelling with other people. Time was when I would eagerly stride off on my own if not simply because it meant I would no longer have to encompass other people, with their own whims and timetables, into my carefully laid plans; nowadays I understand the push and pull of journeying with others and in return they brook me at least some leeway with being at places an hour before we can even access ticketing desks.