I always have a travel knife/fork/spoon set in my case. I’ll frequently get an M&S salad, chicken, fruit, yogurt etc. for dinner rather than, yet another, restaurant meal or room service.
A wash bag that is ready to go with everything I need stays in my case - no decanting/sharing toiletries from the main bathroom. I also have some make-up duplicates to save taking my usual make-up bag. Very random but I also have good tweezers with me - hotel bathroom lighting is brilliant for doing eyebrows! I also make sure I’ve got some emergency drugs in my wash bag - paracetamol, packet of Lemsip, Imodium, gaviscon etc. - anything that might be tricky to get hold of if you’re not well while you’re away.
A good water bottle and thermal coffee cup. Coffee bags and/or good teabags are a game-changer compared to hotel sachets of Nescafé.
Someone’s already mentioned chargers and extension leads. If you’re going to be in the car an ‘emergency kit’ is helpful - change of clothes, shoes, some toiletries (including tampons).
Depends on your work but as a regular traveller I tend to stay in the same hotels - that makes a difference, especially if they have a gym or pool. I always try to get outside for a bit - it’s very easy when travelling to go from airport/car to office to hotel and back - a 20 minute walk in the fresh air makes a massive difference to my wellbeing.
Make sure you know your company expenses policy inside out - partly so you claim everything you’re entitled to but also so you don’t get caught out.