What do you wish you bought sooner?

First of all hello there newbie here. My wife and I are close to picking up our new Cougar 5th wheel and since I inherited my dads old truck that had everything needed to tow a 5th wheel the dealer gave us $400 to spend in the store at the dealership instead of a brake controller and hitch and the first visit is on the salemans discount pricing. So my question what have you found as being a wish you had bought sooner. I have heard a longer main power cord is a definite as the one that comes with the trailer might not always be long enough. I know TP and all that other stuff but what were the nice to have things that would be useful? Thanks in advance I have read a lot on here and hope to contribute some too.