Market exchange rates are better than the official exchange rates applied by banks (more than 10% difference in the case from US dollars to Laos KIP now)
U.S. dollar cash is king in tourist areas. For short trips, bring U.S. dollar cash for expenses and exchange small amounts into KIP as needed for admission fees to government-controlled destinations and at local stores and restaurants.
Currencies other than the U.S. dollar and Thai baht are usually at a bad rate at money changers, so it is better to exchange them for dollars in your country.
Credit card cash advances are available at ATMs, but at official rates lower than the market rate. Only KIP can be withdrawn. It is dangerous to carry more cash than you need, so you will need a credit card as a backup.
Laos is still pretty much a cash-based society. Unless you’re traveling at the highest end, credit card payments at hotels, restaurants, and other stores may be subject to a 3% fee. Outside of the main tourist areas, all payments are usually Laos KIP.