Don't overpack - there are two places to do laundry on the trip so you really only need 7 days of clothing.
Ensure you bring some insect spray (Deet) many of us were bitten by mozzies.
Bring a 32gb usb memory stick as Mr Black (see above) is happy to put all of the photos / videos of the group on it for you, alternatively he does put them on facebook as well.
When you go to the Cu Chi tunnels, there is the opportunity to fire some guns at a firing range, you are offered the empty shells as a souvenir, but as I found out at the airport on departure you will most likely be stopped and have them removed (slightly worrying at the time)
As you will be visitng three countries an exhange rate convertor app on your phone would be useful.
Bring a day pack for carrying your essentials, cameras, sun lotion etc, but you won't need to cycle with it (leave in the support vehicle) we had regualr stops when cycling and the refreshments provided - fresh fuit, choc bars, peanut brittle etc and cold water were plentiful. There are also rehydration sachets available so no need to bring those.