First thing you should know about supercharging: power is shared between pairs of adjacent stalls, so if one of the paired chargers is in use and you take the other one, both of you will get a slower charging rate. Take note of the charger number you are about to use; it will be labeled (1A, 1B, 2A, 2B, and so on.) If you can, try to pick a stall where nobody is using the other charger in the pair. For example, if somebody is charging at 1B, but 2A and 2B are open, you should go to one of those, not 1A. If the supercharger is busy, then you can take whatever spot is open first. It's a lot like the Man Rule about urinals.
You should always have snacks and a bottle of water or two for each person in the car; this is a long, hot drive. For emergencies, I've got the Tesla roadside assistance number and my mobile phone (plus AAA card, and I carry the tire repair kit as well.) Bring along your UMC in the trunk, even if you never need it.
Use the car's Navigation system to set a route to your destination (or alternatively, to the next supercharger). This will show you if any of the superchargers are offline and you need to avoid them. Don't be concerned if you pull in and all spots are taken; the wait is usually pretty quick. Which leads me to this piece of advice:
Don't try to arrive at your destination at a particular time. (If you need to arrive by a particular time, plan ahead so you leave yourself a large buffer in case the wait for a supercharger is unexpectedly long, or the power is throttled on particularly hot days.)
Autopilot on the 5 works great! It will leave you feeling far less tired at the end of the journey.