What kind of trips have you taken so far? Any other weekends, vacations to draw experience from? You'll learn a lot during that 2 months, no doubt about that!
Make sure you have a pad of paper and pen, so you can write down all the things you realized you forgot. The good news is that Walmart is everywhere, to allow you to stock up!
Black tank wise, use plenty of water when you flush. Half a "pot" goes down with any solids. I don't worry about blank tank sensors, they never seem to work right (probably for the reasons Seilerbird mentioned) but after awhile you'll learn how many days of use it takes to fill up before you need to dump it. Probably not long on a Class C (depending on tank size) and family of 4... although only 3 using the pot. Monitor your 3yo and make sure he or she doesn't flush too much TP. Tank sensors aside, that'll cause a big clog when you try and dump if the TP ratio isn't greatly outweighed by the water ratio.