Just back from Viet&Camb Xmas/New Year trip. I changed sterling to dong at the hotels in Vietnam and got a good rate. You really do need some dong as you go along. I also brought some dollars and found $1 were handy. But no point in getting dollars to change to dong as you're changing money twice. The hotels were better exchange rate than airport, banks or money exchanges.
It was cold in Hanoi/Hue/Hoi An in Dec so pack an extra cardigan or fleece. Also would advise to bring some cheap surgical masks, even to use on the plane, as over half of out group were ill at some time or other, and a few after they got off the plane. Masks also good for wearing on the streets to keep out the scooter fumes!
