Most people now go a mix of cash, credit and debit cards and travellers cheques. Laos has no ATMs, so you need to rely on exchange booths and will need to manage your money a bit more carefully than in say Thailand, where every corner has an ATM. You can get an advance on a Visa card in most major towns, but need to go inside the bank during its limited opening hours. For cash, bring US dollars or baht, which you can exchange nearly anywhere, and occasionally use directly.