Boiled veggies, yo!!!

I love boiled vegetable medley for holy grail turds haha.
I get the vegetable medley prepackaged in bags (because I'm lazy -- you could of course just as easily buy broccoli, cauliflower, carrots, etc. separately) and boil 'em with some broth.
Rank this one high on the fiber, flatulence, and soft stool meter, but low on the flavor meter

Still, it was and still is a staple of my patent-pending "No Mo' Fissures Diet".
Ok and the shorter answer: eat whatever you've been eating that's led to soft, regular stools. Honestly I wouldn't make any drastic changes just because of surgery -- keeping up any established routines is best IMO, but for extra "protection," a heaping helping of boiled veggies can't hurt IMO, particularly in the first few days when folks tend to have a tendency to be a bit "clogged up" from the anesthesia (just be sure not to over-do it and cause the runs obviously).