I'm planning to go out tomorrow to do "Bulwick and back", a ring of 60 caches. When things are going well, I'd expect to do about 10 caches per hour, so I'll probably set off at 11 and get back at 5.
At cache 31, the route crosses a road which would take me back to the car in 4 km, which isn't a long way if you're on a bike and tarmac, so I could break the ring into two if I do an extra 8km on the bike. I'm not sure yet; the alternative is to take enough batteries to do the whole thing in one lump. I think I'd need three batteries to complete the route, which means that I'd take four, plus lighting (in case it takes a lot longer than I think and it gets dark, which is at about 6:00 or 6:30 now). And a bottle of water, and the usual emergency kits for A) the bike and B) me.
So what I'll do, is take enough supplies to do the whole circuit in one lump, but when I reach cache 31, I have the option of changing my mind.