For rides 90 minutes or less nothing unless I leave fasted (I hate riding fasted BTW.) For 2 hour rides around dinner time I'll eat 200 calories of fig newtons or something similar. On my 3-4 hour weekend rides where I leave an hour after lunch (i.e., well fueled) I'll eat a Clif protein bar. Mostly I'm eating so I don't get hungry. If I start getting hungry, which is hard for me to detect on the bike, I get sluggish by the end of the ride.