What should I do to my 2018 stock tundra?

Otherwise start with useful stuff:
Diff breather mod since you launch a boat. - You NEED this.
TRD Rear swaybar. - You NEED this, it's a dealer option so it's "Stock"

Does not affect value of truck, saves rear dif issues, increase ride control and safety.

 

HAHAHA

Chrome rules!

Black emblems/paint/interior is terrible!

Especially for things that live in the sun, where it is warm 1/2 or more of the year.

 

Let's see... I did these over a few months to my 2018 Limited (I think this is in order):

1. Side steps
2. Organizer tray for the console
3. Soft tonneau cover
4. Cargo bed extender
5. Bed mat
6. TRD gearshift knob
   
7. Stick-on doorsill paint protectors
8. Stick-on black letters for the tailgate
9. Spray-in bed liner
10. Vent-ring covers to hide the chrome (I kept getting reflections in my eyes)
11. Under-rear-seat locking storage
12. Front husky mats
    
13. Stick-on window rain shields

Bought, but still to be installed (waiting for good weather)

1. Bed step
2. Rear sway bar

All told, it seems like a lot, but some of it was used/Craigslist, some of it was on sale, some from eBay. I think the only thing I paid full market price for was the Line-X. If I do anything else, it will be the pop-lock for the tailgate.