12@400+ mile days is one heck of a drive. Hope you have a great time!
If you average about 75 MPH overall you're going to need nearly 70 hours of music to do that distance and not repeat...
Anything you think may melt should be in the passenger compartment with you - deodorant, emergency candles, chocolate bars, etc. Storage areas get too hot.
Coppertone makes a dry spray suntan lotion that works well to keep from getting the goop on the steering wheel, etc.
Obviously, cell phone is a must and your Porsche roadside assistance card (if they still bundle that with the new car) or AAA. One thing that may not be obvious is that you may want to have more than one cell phone - network technologies vary in many off the main drag/out of cities locations and with a single-band phone you're going to see a lot of "no bars". You can get cheap (~$20) disposable phones with GSM or CDMA or TDMA network coverage from
www.tracfone.com or similar if you want to be sure to have at least some signal coverage nearly everywhere (if you go for tracfone, PM me and I can get you some free additional service time).
Duct tape and a metal coat hanger (or heavy gauge electrical ground wire). Universal fix-it supplies! (Hopefully not needed for the car, but you never know what else could need fixin'!)