I concur with Teigyr.Build up you mileage the best you can.If you can get to 70 miles ,then you should be able to push on for the big 100.Pacing is probably the biggest deal.Cycle at a pace where you can still converse with friends. I was doing a solo century last year and I had a package of those shot blocks.I was feeling a little draggy so I thought I'd try one. It was pretty good. I was bored a little later down the road so i had another. It was really good. After the third one went down I got a little sick. Then I blew.Literaly. Just go with what works for you. Keep hydrated. Use sun screen.Make it your great adventure and you'll do just fine.