At least 90%, probably more, of the flights I take these days are e-tickets, where you get the paperwork issued to you at the terminal on presentation of proof of ID. It is quite unusual to have to worry about a paper ticket as I rush out the door.
Because it is much easier to get money out of an ATM on arrival, and in any case credit cards are almost universally accepted, I literally cannot remember the last time I went to a bank to get foreign currency before I travelled. Of course, a lot of my trips are to euro-zone countries anyway, so I don't even have to engage "foreign money" gears in my brain.
Of the three, passports remain essential for most international travel. Yet here again, at least in the EU, things are shifting: my flight this morning from Brussels to Ljubljana is within the Schengen zone, so if my Belgian ID card had come through (I'm still waiting for it) I could have left all my various passports at home. If the American authorities were smart, they'd be looking at how to work towards some form of similar arrangement with other countries, rather than continue to inflict ritual humiliation on us at immigration.
In fact, these days it is not so much about what you should remember to bring, more what you should remember not to bring. Specifically, fluids in the hand-luggage; I've lost several cans of shaving gel to airport security in the last few years, not to mention the Macedonian wine confiscated because I was not going to risk packing it in my suitcase to get broken in the hold. It's not just fluids of course - Rosi challenges us to identify a way of hijacking a plane using nail clippers - but that is how it has affected me most.
Hopefully the next generation will catch themselves on about security without losing the conveniences we have accumulated over the last few years.