I usually carry a Clif Bar. I used to eat it at 30-40 miles into a 50-65 mile ride. Now I find I don’t really need it up to 60-65 miles, assuming my normal breakfast. A couple weeks ago I did 90 with just the one bar, that was a first for me. On other centuries and double metrics, (my longest), they were supported and I tended to eat real food. This included bananas, watermelon, Oreos, fig Newtons, PB&J, bacon, trail mix, soup, chocolate chip cookies, oranges, chips, breakfast burritos and probably some other stuff I can’t remember. Not all of this on one ride, of course, and not a lot at any one rest stop. On those supported rides I finished with my bar still in my pocket. IF you like Clif bars, go for it, but over 290 miles I personally would mix it up with other stuff.