It's always safe to bring 2 tubes. I have heard horror stories about double flats from people and the only double flat I've ever had is because a mischievous student let the air out of my tires while my bike was parked at school.
My first real group ride was a century, but I did not prepare well and I was completely alone for the majority of it. Here my exercise in stupidity in bullet format:
- I did not stretch the night before or the morning of
- I decided in all my brilliance to drink the night before
- I did not eat real food prior to the event (it started too early and I was hungover)
- I did not pace myself-- I struggled to keep up with all the hammerheads for a while and then burned out
Back then I didn't really have anyone helping out with these things. Granted, it was my own decision to throw common sense out the window. It would have been nice if someone had been able to give me pointers before the century but they hadn't. All I knew is that I'd been on 75 mile rides before and hadn't done anything special to prepare and this would probably be the same. Ugh!
I have learned a great many thing since then!
Soooo... have something to eat that has carbs and protein about 4 hours before your ride. I am doing a 50 miler today, so I am having some steel cut oats with maple syrup, nuts and dried fruit.
Pack something to eat for the ride-- easily digested carbs. Bananas are great!
Stretch beforehand
Do not go out with friends the night before
Good luck!