Well I did not have the same surgery you had, but a few years ago my colon ruptured and I too had to have a life saving surgery. The doctor advised my wife she might want to start funeral preparations just in case. Needless to say I survived, but without 10 inches of my colon. Since then I have found a lot of different foods I can no longer eat. Food goes through me a lot faster then before. A few of my favorite foods I can't eat anymore like eggs and mayo. I used to love both of those, but now I'm running to the restroom literally minutes after I eat them, so I don't eat them.
Before a ride I'll have peanut butter and jelly sandwich on wheat toast. I'll take a cliff bar with me in case I get hungry. Post ride is a peanut butter banana sandwich or a flour tortilla with peanut butter.
Just keep at it, you'll find your rhythm and find what works for you.