One thing it's easy to overlook, weird screws.. Our trailer was assembled with square drive screws.. I purchased a small screw/nut driver kit from walmart/home depot or the like that had square drive. Eventually found that all of the screws used the same size driver, and purchased a quality driver in that size as well.
As mentioned by others, think about the process..setting up/tearing down/dumping tanks (watch youtube videos if you're not familiar with these processes). Also think about things that can go wrong on the road, flat tire for example.. If you are capable of changing a flat, make sure you have the tools necessary. Tire plugs and portable 12v compressor if you're comfortable with that as well.
You may find (as we did) that your first few trips out you'll keep finding more things you 'need'. Then after a few years you'll start thinning things out, the third time you move and item you don't use to get to something you do use..probably time to remove it.