I second Oak's post. It's really easy for me personally to not get enough on the bike and afterward--I need protein, a mixture of complex and simple carbs, and caffeine after a ride. DBF eats pretty much everything that isn't nailed down after a ride. (Okay, I do too, but I at least leave a few things!)

Sleep is the other thing--it's not so bad now that I'm used to going out around midday, but when I get up at some unreasonable hour to ride, I will manage to fall asleep sitting up. I have a hard time making myself go to bed early. Total nightowl here.