I tend to keep it very simple.
My last 2 outdoor rides have been 110-120k (so 3.5-4 hour efforts, average power high-ish Z2) and they have been fuelled by a large bowl of cereal and a couple of espressos for breakfast, a large bag of jelly babies on the bike, and 2 bidons of water with electrolyte powders.
I made sure I sip from the bottles every 15mins or so and had 2-3 jelly babies every 20 mins or so. On a hot day I’d need to stop somewhere to refill the bidons.
If I was going much longer than that I’d probably stop via a cafe, refill the bidons, and get another espresso and a slice of cake 