I'm just back from my very first 400 km (actually 418 km) completed in just under 24 hours... And it was hard... Much harder than the 300 km brevet I did 3 weeks ago!!!
First thing I did wrong: started too fast for the first 150 km, my friend and I paid for that later!!
Then second thing: eat a pizza at dinner... It just didn't work, and we spent the whole night feeling like throwing up (my friend actually did throw up in the middle of the night) and consequently we didn't eat during the night and had a really hard time making it through the night!
The good things now: my lights system which worked really well (the NightHawk halogen and the EL500 Cateye for the downhill plus the headlight to fix my friend's puncture in the middle of the night), and a great hour of "sleep" wrapped in a space blanket at the bus stop... great memories...
Other interesting thing: I didn't know you can get REALLY sleepy on a bike... Always thought that you would feel OK even with the lack of sleep because it's outside, there is fresh air and you have to stay concentrated... But during the night it is very dark around and it gets tempting to close your eyes sometimes...
Anyway, I'm done with my pre-PBP brevets, and I've done a few mistakes I won't do again next year!
Now I'm not doing more than 250 km in one day for the rest of the year!!!