Other than the obvious low cost things that have already been mentioned (which I would also include silicon spray and dry-lube for the slide out), I agree with bradnailer about gettting a good quality weight distributing hitch that includes sway control. The two most popular are the Equal-i-zer (notice spelling) and the Reese Dual Cam. There are much better units, but the cost of them triples.
As mentioned, chocks for the wheels (for stabilization when parked) and a surge protector are also very important. To make life a little easier, I would also look into getting an electric tongue jack....best investment I made with my TT.
Another good (but not necessarily required) is to put two 6v golf cart batteries in place of the cheap 12v deep cycle that comes with the TT.
There's more, but you'll determine them as you go along.
Whew! Getting expensive, huh?
Ron