As you go you will build your must-haves. Some are ones you find along the way and others not as much. One great item that I love is the TripMate Elite. I use it in hotel rooms and media centers(I am a motorsports photographer).
Hotel that has a hard line you plug it in and it creates your own wireless network. Put all my devices on it and get great internet most of the time.
I also have 2 sets of toiletries that stay in bag. Works great to always have everything which is important. I also echo the go slow. I don't show up last minute to airport and rush through. I spend 20-30min in the SkyClub enjoying the view and relaxing a bit. When I arrive I don't rush to the baggage claim and then rental car counter. It's just not worth it to be stressed out like that. Book the slightly earlier flight and have the spare time to not be rushed.
And I echo the choose a single or a couple rental car agencies. Even their basic tier gets a 'bypass the line' and go get into car. Or choose your airline and many give great status. Save the time 'for free' where available.