If you choose to stay at the airport, you can buy food and goods in restaurants or shops at the airport. Restaurants and shops at airports usually accept Vietnamese dong and international credit cards. You can also exchange some Vietnamese dong at the exchange counter at the airport, so that you can shop at the airport.

If you choose to leave the airport, you need to go through the visa formalities (if your nationality requires it) and leave the airport through the customs exit. In the center of ha noi, you can find all kinds of restaurants, shops and scenic spots, but please note that you need to spend some Vietnamese dong to pay for food and other expenses.

In short, you can choose to stay at the airport or go out to explore local culture and food, but please make sure you have enough cash or credit card to pay your expenses.