It pains me to bring it up again, but this is more than a first world problem, its an STW first world problem….
You don’t need anything special at all to ride 100 miles on a bike. It’s a few hours of relatively gentle exercise, so eat whatever you fancy. Even if you are cracking on, just eat something that you can fit in your pocket.
You won’t die.
It’s just riding a bike.
Edited to say: my Granny and Grandad used to ride to Blackpool on a Sunday, have lunch and ride home. It’s a 120 mile round trip…