-Lights for the windows along with a timer in case I am not in the room.
-Power strip - Even solo, I like to plug that puppy somewhere and just charge all my stuff on there - Camera, phone, etc. Defo important if you go with more than just yourself.

Disney has outlets in many parts of the rooms but, they are in hiding. Hehehe.
-Mini Lysol (or big Lysol) (found at the travel section of most places) just to spritz the air vents and freshen the room a bit between Mousekeeping visits. Also works to keep shoes smelling fresh! I also spritz the bed sheets.
-Wipes - Both the Lysol/Bleach kind and the ones you can use on yourself. Regardless as to how clean the hotel is, I like to wipe down hard surfaces. Especially if I am going to eat on them. I'll use the Lysol one to wipe down the remote which is sometimes very gross.
-Lip balm or body glide - Apply to feet, prevent blisters.
I drive up so, I know some people can't do this unless you ship ahead but...
-Small coffee pot if I stay at the Values. And coffee of course! I LOVE coffee... HAVE TO HAVE coffee . Before last year I would get the resort mug and have my heart's content of beverages but, since I do not drink sodas anymore, I can't justify paying for only coffee. (Mods and up have coffee pots in the rooms)
-Air Purifier - Not so much for a smelly room (which in 20+ trips I only had ONE musty smelly room) but for the noise it makes which drowns out some of the resort noise. I am not a light sleeper but, I need dark and quiet to fall asleep.