If the OP isn't talking factory options that you can order (okay, okay, it is more than 5 tho.):
- shocks on the trailer (a very few brands come with them)
- EMS (Progressive Industries) and permanent LED voltmeter inside (this is basically a must-have for CGs with power hookup)
- autoformer
- next load range up in tires (ours were a factory option)
- laptop & Verizon mifi hotspot
- RV GPS
- WDH better than basic bars & friction bars (we use a Reese DC)
- getting rid of the Lippert jacknife sofa and replacing with Harrison double recliner with power recline
- Torklift entry steps
- Stromberg Carlson soft grab entry handle
- built-in vacuum cleaner (ours is Intervac)
- replacing WFCO converter/charger with a Progressive Dynamic unit & AGM battery
- backup camera (although not impressed with our Garmin camera)
- satellite TV setup
There is an endless list of misc. straightforward simple lo-cost mods & upgrades that can be done that you will decide you want along the way.
If you have the option of ordering options on a new TT, the various manufacturers have many different offerings (some of which are "forced"). Our top ones are solid surface kitchen counter, electric awning, 2nd Fantastic Fan in bedroom, electric stabilizer jacks (except they don't actually stabilize) and fiberglass front cap.
My no. 1 favorite "option" is a DW that understands hand signals when backing into a site. Everyone should have one. :)