Make sure the location you are planning on visiting is open. Nothing is more of a bummer than driving two hours to find your location is closed, under renovation or out of business.
Have a rough idea of how to get there and the address. Cell service can be spotty in rural areas so don’t count on your magical phone to get you there.
Pack healthy snacks. You probably won’t eat them, but you can at least feel virtuous and smug.
If you want to have lunch while road tripping, plan to eat first. Many cafes in small towns close by 1 or 2 on weekend afternoons.
Always have some cash. Many places are free/free-will donation. Be polite and help support them with a donation. You may also find a nifty shop or bakery that is cash only, too.
Be polite. Ask if you can take photos, don’t wander on to private property, don’t touch things, don’t let your children run amok, etc. Use common sense.
Leave time for wandering. If you see an interesting building or winding road, go check it out. Stop and walk through the town you are visiting. Pull off to see the county park or local historical museum. Road trips are for relaxing and seeing new things, so calm down and enjoy your day.