I would say it will be tough. It's quite a jump from going on one 20 mile ride to riding 90 miles. Even with stops. What is the terain is going to be like?
Bring water, maybe gatorade or some other energy drink. Eat during your ride so you don't bonk. I found powerbars to be an ok food. Only have .5 saturated fat, and don't taste too bad.
Main thing try going your speed. If you can hang with someone thats great, but don't push yourself too hard trying to hang on to someone who is faster then you.
Also don't forget to have fun.
