Your wants and needs will come into clearer focus once you have the TT. I'd look at the various online RV parts & accessories vendors to see all the "stuff" there is available. It will depend somewhat if you plan to camp mostly close to home or plan to get around the country. If planning to buy much, I'd shop all over the internet to get the best prices. CW can be the worst. Amazon and ebay can be high and low depending on what it is. Tweety's, MakariosRV, PPLmotorhomes and more can be pretty good, but shop around.
There are some basic must-haves as listed above. Did tire pressure monitor system get mentioned? Then there are some really gotta-haves to improve creature comfort & experience like a decent foam-topper mattress (highly recommended), anti-gravity recliner, built-in vacuum, sat TV, quality BBQ, 4G mifi, etc. As you become a more seasoned RV-er (maybe after 1 season??), you could find there's lotsa cool stuff you can do and things to buy like Dexter EZ-Flex, AGM battery(ies), better WDH, cover for the off-season, water filtration, RV GPS, quick connect mod. for BBQ, etc...
If you're a handy DIY-er type person, there's an endless list of mods that can be done from minor to major but you'll figure this out as you go and find out what would help in your particular TT and as you read about other owner's mods on the forums.. I think one thing most TTs need is another shelf in upper kitchen cabinets and would count on doing this.
Some of my personal favorites: Dexter EZ-Flex + wet bolts, shocks on TT and HD ones on truck, La Jolla plush recliner, Weber BBQ, Verizon 4G mifi (pay as you go), Fantastic fans (bedroom & bathroom).
What types of CGs do you plan to use? Boondocking and/or full hookup CGs? There are some membership organizations that work well for some. We like our Thousand Trails and bought it pre-owned off CL for waay cheaper than "new". Note that some CGs can be petty hard to get into during the high season and you should book as far in advance as possible but this isn't always possible. You could end up having to dry camp in some busy CGs so may want to be prepared to have no power, water or sewer.
Most importantly - have fun! ;)
