What form of money should I bring to Vietnam?

I am a student traveling from America to Vietnam in a few days. I am on a pre-paid trip, so all of my hotels and base meals are paid for. We are in Ho-Chi-Minh city, as well as some very rural areas down into the Mekong River Delta. I only need money for meals/souvenirs and stuff, and I am supposed to bring about $300. What form should I bring this in? Cash? Travelers cheques? Debit?