What to buy:
Strongely I suppose you to buy local postcards, the real gift from Laos.
1 PC= 5 THB.
There is also post service:
Postage to Asia 40 THB and to Europe 45 THB.
The sales will help to you have postage on postcards and stamp air-mail on them.
Then you can put them yourself in post-box.
Laos souvenvior shops sell stuffs the most are as the same as these in Thailand, such has bags, scarfs, decorations, neck laces etc.