I can normally get by on a 2 hour ride without eating, just water with a SIS tab dropped in. I make sure I'm fueled up well beforehand. For 3 hours I may take a banana in with me, and/or a nut bar but as I'm not looking to push hard I'm hoping my fat stores start to come in to keep me going.3-hours is long time on a saddle, indoor and outdoor. Refuel is vital in that kind of long training session, better take enough drink and energy gels and bars next to you or banana or at least something to eat.
I used to take an energy gel before a race on bkool or zwift, but I think they were just placebo's as I can't believe they helped much in a 60 minute race