There's probably loads of solo-ists on here that are super fit etc etc etc. and drink all the torque drinks and energy bars and what not, and they'll chip in with the 'pro' advice.
But i'm no one of them, I do cycle a reasonable amount, ( to work and at work ) and I do on occasion enter into daft things like you've just done.
My experiences from being a daftie at these things…
If its a lapped event, and assuming a 1hr to 1h15.min lap time ( ish ) then take a break after each lap. 10 to 15mins. Be realistic, you're not going to win it, so you may as well be able to stay the distance and last the time. Taking proper breaks early on makes a difference further down the line towards the end of the time.
Drinks … take plenty. To be honest, I normally just drink diluting orange which i make on the sweeter, more concentrated side. The fancy mineral drinks sometimes make me boke when i'm working hard. An alternative I tried was to put Berocca tablets into water as a mineral source …. its only minerals and vitamins after all.
Food … I find forcing myself to eat a snack at each break helps too. Banana's are good. I dont buy the expensive energy bars. I personally buy the cheaper cereal / breakfast bars. Best of all I think are fig rolls. Not too sweet, nice n chewy but not too dry either. As already said, i'm not out to win and a baw-hairs worth of a difference given by a stupidly expensive bar or gel isn't worth it. Fig rolls FTW. !!!
Training wise, longer rides and pushing out the stamina levels really as already said. MOre a case of just getting out on the bike and putting the time in so you're used to expelling effort over a long sustained time. Speed aint an issue, keeping the pedals turning through to the end is. Also, make sure your bike is comfy after long long periods. I found that a setup of a bike I liked for short blasts turned out to be sore on the back after a longer number of hours.
