Another vote for dry shampoo. I love the stuff, I use it regularly even when at home. I really like the Klorane, although it's a spray. I used to swear by the Oscar Blandi power, but I can't seem to find it anymore so maybe it's been discontinued. Looking for a new powdered one, so open to any suggestions or recommendations.
I always bring a few folding travel hangers and clothespins. They hardly take up any space and I can usually slide them into a shoe when packing. Good for letting clothing air out or hang dry after being washed. I found some cute brightly colored hanging clothespins - they have a hook at one end that goes over the shower pole, great for hanging socks, undergarments, etc. I also like to bring 1-2 inflatable hangers which are great at helping heavier pieces of clothing dry; after the hanger is inflated the back and front of the shirt are held far enough apart that it gets more air circulation. (I wear a lot of merino wool and prefer to hand wash it myself when needed rather than trusting the hotel laundry.)
Makeup removing cloths like the Magic Makeup Eraser. They do a great job removing makeup using just water. I'll usually bring 2 with me so I always have a clean/dry one. I bought some travel sized ones last year in Ireland, wish I'd bought a few more of them.
This might seem like overkill, but I nearly always bring a bathrobe with me. The hotel-provided ones almost never fit (I'm very busty). I really like to lounge in my PJs/robe at night while reading or watching a movie and drinking tea (or wine!), and keeping to this routine when traveling helps with my sleep schedule. I'm often away from home for 4-5 weeks at a time and I value the little things that make living out of a hotel/suitcase more civilized. Plus, I like having a robe that fits and covers me for the sake of modesty - ie, room service comes earlier than expected, one of my colleagues asks if I have any decongestant, or there's an emergency and we have to evacuate. (I've had this happen 3 times. Twice, I was in bed asleep and the 3rd time I was in the shower.). I found a lovely, lightweight merino wool robe. It's cosy, doesn't take up too much space in my bag, and is suitable for most climates. I've also used it as a coverup en route to the hotel pool.