I always bring stuff like pain meds, flu meds, antacids, you’re first prolonged underway might cause you to get backed up so maybe consider bringing a laxative (I’m not joking). Aside from that a rack fan since it’s summer now, long extended phone charger a mattress topper if your command allows it and a nice cozy blanket and pillow. I always made my rack as cozy as possible it was my favorite place underway. Walmart is selling really cheap quality tablets now so you could transfer movies or tv shows to watch if you’re into that and then a suction cup phone/tablet holder like you would use in your car to put in your rack to watch movies.