Andrew,
Prior to joining the club, over a 2 year period I think I did about 8 x 200km, 3 x 300kms and 1 x400 km rides. I also started a 600km ride but gave up after 200km. No motivation, not feeling right, (HR too high). With hindsight it was mostly mental and a handy train station. I was planning on having a crack at Paris-Brest-Paris, which has just finished. But my failure at the 600 showed that maybe I wasn't ready. I then joined Addiscombe to do something different so some good came out of it
The most I ever carried was contained in a Carradice SQR bag that I use for my everyday commute.
Food wise it was never too bad, you are never more than usually 40 to 50 miles between checkpoints that will have food. I usually used to carry some sandwiches for emergencies and fig rolls. I tried energy bars but after about 8 hours they get a bit much.
The most important thing is a tool kit and enough inner tubes. I have experienced a snapped chain and four punctures before, on seperate rides I have to add.
The time contraints on most rides are very generous, max average is allowed is usually 30 kph and the minimum 12 kph I think. Though that of course is overall time and the clock is always ticking so if sleep is required it needs to be built in. To give you an example the 400k I did went from Chalfont St Peter in Bucks to Chepstow and back. I did that in about 20.25 hours. Some people stopped for a sleep a some point and took over 30 hours. Horses for courses really.
I think Audax riding has got a bad image ie old men with beards riding tourers (there are a lot of them). On the other hand the chap I did my 400k with was younger than me and was riding a £3.5k Specialized Roubaix.
I have enjoyed my racing this year but I have to admit that I have missed seeing various bits of the south east and other bits of England on my travels.
The big disadvantage of the long distance stuff is the obviously the time. I have three young children so to give you an example I got home from the SCCU 50 by 11.30am. To do just a local 200k I would leave home at much the same time but would not get home much before 6 or 7pm.
Hope this helps
Dominic
PS I am working on the beard