290mi in one shot? Over a couple days?
Either way, I would defer you ask one of the randonneuring (spelling?) guys on the forum. I thought nutrition for that was a bit different and might have involved more focus on 'real' food at some points along the way?
I stick to Cliff Z-bars, the kid's version. I find them easier to chew and eat while not stopping riding. I sometimes will reach and open on the the roll. Or at a stopsign will open it then keep rolling to eat it. I couldn't really chew/eat the full size Cliff bars so well like that. It seems custom rice cake recipes are in vogue again also. I ain't got time for that. But people seem to love them for the nutrition you can pack into them.
I hate Covid. I miss my long ride days with the coffee/pastry stop and a crew. Sigh. Maybe come cooler weather and fall I will take my mini backpack with a mini thermos and a treat.