Some of this post was inspired by Andrew Godwin's travel equipment 2019 article.
Fresh back from my long USA trip, which was followed by two shorter domestic ones, I thought I'd write up a few Rules To Live By when it comes to travel. In addition to the personal stuff, I've done an increasing number of short-haul 48-72 hour business trips over to continental Europe in the past year too.
Keep a permanent "travel set" of as much as you can
Obviously, this one depends somewhat on your budget. But let's start with the basics: things like toothpaste and toothbrushes aren't going to cost you any more (in the long run) to keep an extra set of. Probably the biggest win with all my trips this year has been having a permanently packed washbag: it lives in my hand-luggage-sized suitcase and saves me having to grab anything from the bathroom except perhaps my electric razor.
The next thing, as per Andrew's post, is plugs and adapters. I still have a mixture of USB-C and micro-USB charging on my devices, so I carry a mix of cables plus a plug which goes into the wall or into a car "lighter socket" and outputs a couple of USB ports. I also carry a UK power strip, which means I only need the one EU/USA travel plug adapter to ensure I have four UK sockets available (watch the total current on this one - it might not be a good idea to run a hair dryer off such a setup). This is also the antidote to cheaper or un-modernised hotels which don't have enough sockets and/or have the only one in completely the wrong place in the room.
Since I rarely go far off the grid, I carry just the one small USB battery pack which is pocket size, and suffices to top up my phone in the event of an extra-long or extra-phone-heavy day. Activities like camping tend to be UK-based and involve my car, in the back of which there's a car battery booster which also has USB ports and a big capacity.
Work are also generous enough to provide three power bricks for my company-issue laptop: one for my desk at the office, one for home and one for travel. Don't be shy about asking your employer for the same; if they're smart about their procurement they ought to have spare adapters lying around the place anyway or be happy to have more.
That's about as far as I've got, but I'm pondering keeping some clothes in the suitcase too so I can just grab it and go for the short trips and weekends.
One other tip for the travel set: go to your local Boots (or whatever) and buy toothpaste, contact lens fluid, etc. in small enough sizes to get them through airport security as hand luggage. It's cheaper to do this on the high street rather than get ripped off at the airport. You can even keep it all packed in a transparent plastic bag to make going through security as quick as possible.
Be religious about not packing too-big fluids in your hand luggage: inevitably, you get away with it about two thirds of the time, then it all gets confiscated right before you need it most (why yes, I did lose my sun cream at Newark, and I am bitter about it not being a problem on at least three flights prior to that one).
I haven't got as far as a travel router yet - second best on this is to ensure you have data coverage on your phone, and use it as a hot spot. I do have a cheap and cheerful one on order though, as it would be handy to be able to use a Chromecast etc. with hotel televisions.
One thing I did make extensive use of in the USA was my UK-based VPN (lots of providers are available; I run my own). In addition to securing all the traffic from my phone and laptop when on hotel WiFi, this also ensured I could access the UK versions of sites including the BBC News without adverts or an American slant.
It's got to be the Kindle (or equivalent e-reader device). Lugging paper books around is a good way to damage them (all books are sacred!) and they're heavy.
I have a cheap-as-chips Amazon tablet, which is perfect for downloading entire series onto from Prime Video or Netflix (go find that option, it's surprisingly little-known and really handy). This plugs the gap when insufficient internet prevents streaming live.
After hauling a venerable suitcase around the states which is rather heavy in its own right (when empty), I'm considering investing in something modern and carbon-fibre. For all my Europe trips, though, it's hand-luggage-only all the way.