Initially you should have the leveling blocks. Nothing is more uncomfortable than spending the night rolling to one side of the bed or the other, things can get pretty drastic as far as how level a site can be. Have a short bubble level on hand for checking side to side levelness.
A clear sleeve for the tank dump stub so you can see when the tank is running clear so you know its empty of the solids. Sometimes having the accordion type sewer hose support is handy because the park connection is sometimes higher than the ground. If your trailer has the tank rinse then a separate hose for that connection should be used, do not use your fresh water hose for that ever.
I carry just a basic hand tool kit, plastic cable ties, an Eternabond repair kit for any roof tears and a tube of Dicore caulking for leak issues you might find. I have a battery drill for lowering/raising the stabilizers, please don't use an impact drill, it makes way too much noise. Have a few flashlights on hand with extra batteries.
You will discover things you need and want as you camp. Its a never ending process. Happy camping.