A multi-plug with two UK plug sockets and three USBs
Solid shampoo, conditioner & face wash (I use Gruum) if taking hand luggage only
As above with deodorant - stick not spray or roll on.
Buy a sheet mask at the airport for dry skin after flying
Single-use eye drops (my eyes really dry out on planes)
Portable phone charger
Longchamp-style folding handbag
First defence and anti-bac wipes for the plane
Water bottle to fill up after security
Google Chromecast - often don’t work in hotels, but if you’re AirBnb-ing or similar, it’s super useful to cast to the TV from your phone
Thin but warm big scarf for the flight
I also always take my own slippers with me, as I hate the thin hotel slippers you get.