Same as for any race – the bare minimum to get you round a lap. Multitool, chain tool, tube, tyre levers, gas can in an under-saddle pack. Drink in a water bottle. Emergency gel/bar in jersey pocket.
At night I use a dinky Camelbak which the battery for my helmet mounted light sits in.
That's it.
I've yet to work out exactly what those riders with huge Camelbaks carry in them?!
Polluting a pond with chain grease and all manner of other lubes has to be frowned upon sorry There's free bike washing facilities supplied for by Muc-Off so there is no excuse for it.
Fair point but the queue for the jetwash last year was over an hour long. Those riders wiothout second bikes aren't going to waste time stood there when they could be out riding (pushing/carrying…), they're going to wash the worst of it off in the pond. It's not like there was any lube left on the chain after 5 mins riding anyway.