Take a cooler, with drinks and protein snacks and carb snacks mixed. Stock up before you leave, it will save a ton of $$$.
Take whatever your choice of caffeinated beverage is, in the cooler or a thermos.
Get one decent meal a day, at least.
If you can figure out a way to do it, put a potty of some kind in the vehicle. That way you can plan your stops to beat traffic and stretch, not just to pee.
Switch off drivers at every stop, preferably every 2 hours. Take a 10 minute break to stretch your legs.
Wear compression stockings (if you can get them) and/or do heel/toe pumps to prevent leg swelling issues and even worse reduce the possibility of DVT.
Plan your timing as much as possible to avoid rush hours through cities. Leave very early or drive later as needed.
Each person drive at his/her best time of day--morning or night, whatever. Nap in the middle of the day if it helps.
Have both parties paying attention through cities, the passenger does most of the navigating and the driver can focus on driving.
Get the Waze app. Use it and Google Drive to check traffic.
Find the state DOT web sites and check for construction and expected delays ahead of time. Plan your route to avoid major lane closures, or hit them at low traffic times.
Use GasBuddy for availability and pricing. Stick with large facilities for fast in/out.
And most of all, STAY SAFE!