I got a ton of use out of hanging a hydration bladder/camelbak off the back of my seat. Being able to drink water one handed without have to fiddle with bottle caps felt much safer on the road.

Tooth brush, towel, and basic toiletries are nice if you want to get a quick shower at a truck stop.

You can download maps from google in advance in case you run in to spotty coverage. It might be worth getting an old school printed on paper road atlas in case you have any trouble with your electronics

Ymmv, but i have a couple of magnetic "yay police" and other right wing brainworms bumper stickers for driving through hostile territory. Idk if it helps, but anything that keeps thieving rural cops off your tail is worth considering.

Sunscreen! I've gotten sunburn on my left arm while driving for long distances before. I though car windows had uva/uvb filters but i guess not?

Bring some change in case you run in to an unexpected toll road somewhere.

Toilet paper! You never know.

Extra socks and an extra pair of shoes.

I hope you have a fun trip!