Any old bike would be ok, as long as it's not going to fall apart, take a look at the heap that I'm using.
These rides have been done on all sorts of bikes from Bromptons to Choppers and Boris Bikes, so a cx will fit the bill very well.
Just bring a few tools and a repair kit and maybe a spare fold up tyre if you have one. There will be loads of regulars on the ride, so you won't be alone.
Double water bottles and some sandwiches incase you get a tad peckish between watering holes. Muddies are a good idea if it looks wet, but don't sweat it if you don't have them.
Plus you've got a whopping 13 hours or so to get round, so it's not going to be a "go great guns" ride, more of a country jaunt with a grin.
You need to have some lights too, coz that's what the rules says, but that's about it for rules. You can read more about it all here:
http://www.aukweb.net/handbook/handbook.pdf
It's all very laid back with no stressing, just get to the start on time to get your brevet.
