It varies from person to person...the best way to find out is to experiment.
An easy way to experiment is with various gels (one gel + some water) or gel-like solids (chomps, honey stingers, shot blocks, gummy bears etc) or solid food (dates, candies, breads, etc) and on various schedules (every 20-30 minutes, every 30-40 minutes, once an hour, etc.) or liquids (gatorade, heed, hornet juice, etc)
Better to practice earlier rather than later, see what works for you, what doesn't work for you, and what just makes you throw up everywhere.
For me personally, I'm usually fine with nothing or with just water for that 2-3 hour range. If I am carrying food, lately I've just been carrying dates and eating them as I get hungry, but I've experimented with pretty much all of the above. I almost always eat before I run, and whenever I can I eat as soon as I can after a run (even if it's just a banana) to help myself recover. Not eating afterwards is definitely ill-advised after any long and/or hard effort.
Regards,