don't take too many clothes, or pack lightweight clothes. Plenty of places to buy more and there are two places to do laundry, one in Hoi an the other in Nha Trang.
You don't really need Dollars, we took some and if you do take any exchange it to Dong as soon as you arrive in the airport in Hanoi ATM's everywhere so as long as you have a visa/debit you can use that but remember all the charges.....you can draw out normally 2,000,000 dong a time........about £60 ish plus your bank charges, their bank charges and the exchange rate but its still a handy option.
If you are on the group flight and go via Malaysia get some local currency or Dollars for drinks and food.
Take Malaria tablets, Deet 50 or 100 spray and long sleeved shirt and long trousers for the mekong delta as there are loads of mosquitos oh and a sleeping bag liner although the lodge is very good quality.
(the only dodgy accommodation on this trip is the sleeper train although you aren't in it overnight, the journey is about 10 hours and you are in a 4 berth sleeper)
a fantastic trip, well planned with no hassel........the guides are fantastic
.....only negative, vietnam is poorer than thailand and tourism is in its infancy, near some of the hotels and sights there are the usual postcard, fruit sellers shirt sellers etc....they can be quite pushy but just be polite and patient and walk past them and they won't cause you any issues
you will love it....enjoy