I was really only using it while staying with family and friends where I was always able to use an old monitor or a tiny "bedroom/kitchen" TV, but a hotel TV would be fine too (I'm assuming ports aren't blocked). I brought a Logitech K400 which is small, wireless, and has a builtin trackpad. Was also only using it for programming and basic web browsing. I don't recommend the keyboard (keys are a bit wobbly, some odd key positioning and shapes, definitely takes some getting used to, and the trackpad is relatively poor), but I just wanted something I could use for an hour or two a day, and it was perfectly acceptable for that. If I had to use it for a few more hours, I'd just bring a proper keyboard and mouse (weight permitting).

I was confident I'd be fine though, I set it up in advance and used it briefly on the couch with a tiny monitor for about a week.

I strongly recommend taking advantage of the USB HDD boot that's now supported on Pi 4 -- even some 15 year old 60GB spinning platter you have lying around from a long dead laptop is in my experience going to be faster than an SD card. USB3 to SATA connectors are cheap and reliable.

The reason I did it was just trying not to be wasteful. My laptop died and I have no problem getting a new one, but I'm pretty sure I'll need a new one in a year for work -- the problem is I won't know the specifications (even OS, architecture, etc.) that I'll need until then, so I just wanted to see if I could get away without having to guess in advance. Generally I like to buy only when I need to, and to buy the best thing available at that time (within reason), and use that for a long time.