My last big rides have all been in the Canadian Rockies or Montana mountains. Consecutive 100+ miles days. Some nights and mornings are nothing more than fig newtons, trail mix and whatever else I've stashed into my frame bags.
Leaving Banff Ab. at 5:00AM usually means little sleep the night before. Two years ago it rained all night and I knew the next day was going to be cold and wet.
So, some beer and a good dinner.
The next day 110 miles later on a 45# mountain bike full of gear I am none the worse for the wear. Just keep eating when you can and keep going. Rinse.. Ride... Repeat... etc...
IMHO people let century rides put too much mental pressure on themselves. Often it is seen as getting it done as fast as possible rather than just getting it done.