I don't know about anybody else but I can bring two bikes - a single speed for a blast round the woods, and a geared one for a longer ride.
How do you want to spend the day? I'd be up for an early singlespeed thrash round the woods (say 8am for an hour or two), then if others can't get there that early we could do another ride round the woods starting say 10.30 and a longer ride in the afternoon. That way you have a choice of three rides and you can pick and choose