On the plane you’ll be given an Arrival/Departure Card and a Baggage Declaration form.
Hand in the completed Arrival/Departure Card with your passport and duplicate visa application form at immigration in Vietnam. The Departure Card will be returned to you. Keep this safely. You usually have to show it when checking into hotels and will be asked for it in when you finally leave Vietnam.
You should list all valuable items on the Baggage Declaration form, such as video cameras, portable computers and expensive jewellery. The duty-free allowance is 200 cigarettes, 2 litres of alcohol plus perfume and jewellery for personal use. You can take up to US $7000 into Vietnam in cash or travellers’ cheques; anything in excess of this sum has to be declared.
Hand the completed Baggage Declaration form to the customs official checking your baggage, who will give you the yellow duplicate – again, keep this carefully as it is required on final departure. (NB. You have to show your baggage check when reclaiming your luggage at the airport on arrival; the stub should be attached to either your airline ticket or boarding pass.)
Finally, it’s a good idea to make photocopies of your Departure Card and Baggage Declaration form at your hotel and keep them separately, just in case you lose the originals. They won’t be accepted in place of the real thing, but may make things slightly easier.