In addition to the important topics suggested, I would also suggest adding something about dealing with the cold. I saw a lot of riders (and more on videos) who did not appear to have come prepared for the chilly night temperatures - I suspect quite a number bailed because of this.
Sleep deprivation was a real challenge for me on LEL (and ultimately the reason I bailed), but by PBP I had managed to address this in part by bringing a bivvy bag so that I could crash at the first sign of the dozzies without having to risk swerving up (or perhaps off!) the road to the next control (I saw lots of swerving cyclists so guess they were aiming to cycle to the next control in a zombie-like state).
No real excuses for not having enough to eat and drink on PBP with so many roadside stalls (in addition to the controls and various shops, bars and cafes, etc), but on LEL, especially during the night, this could be an issue. Might be worth mentioning that there's no obligation to buy food at controls (especially if you have to spend valuable time queuing for it) and a better option might be to grab food on the hoof from boulangeries, etc where you normally get served straight away.
Best of luck with your friends book.