Cash mainly. ATMs accepting international cards are increasingly available in cities, towns and tourist areas. Bring pristine US bills for exchange.
Tipping is not customary in Myanmar, though little extra 'presents' are sometimes expected (even if they're not asked for) in exchange for a service.
Airport If someone helps you with your bags, a small tip is welcomed.
Restaurants As wages are low, it's a good idea to leave change for waiters.
Temples A small donation is appreciated if a caretaker is required to unlock a temple.