I’ve done it several times, usually on my SS road bike and yes, with a (small) CamelBak. 😳
Holds extra clothing, bit of food, couple of extra tubes and the spare battery for my lights. Not ideal but hey, it’s dark so no one can see the fashion faux pas! 😉
Getting out of London can be a bit mental – stick together as it’s not unusual to get a bit of abuse from drunken chavs as you go out through the less salubrious parts of North London and Essex. Soon quietens down and most folk find their own group at a comfortable speed. Riding alone is to be avoided if possible, mostly cos it’s boring as hell.
The feed station can get VERY crowded. We’ve always battered it the first 40 miles or so to get in there early but equally, some people just ride to a pub and sit there til last orders, using that to fuel up. The last few years there has been someone opened up their front garden to sell bacon sarnies (about the 80 mile mark IIRC). Take a few quid – it’ll be a lifesaver if you need to stop at a garage or for bacon sarnies! The cafe at the beach is a bit meh – it used to be good but was average at best last time I was there. Opens about 5am so it’s not worth caning it to be there at 4 cos you’ll have a long wait on a cold beach!
Travel back: we always rode down to Ipswich (about 40 miles) and got the early train back which usually has a guards van on it and they know the ride is on. There is a local station but trains from it are few and far between on a Sunday morning and there’s less bike space than on the main line.
Good event though: have fun, chill out and just enjoy the sight of people on every type of bike imaginable. Someone even did it on a Boris Bike last year.