If there is something you absolutely have to do in Vietname is to take the time to have some coffee. There is definitely a strong coffee/café culture. You will a lot of people sitting on the sidewalk terraces sipping coffee, chatting away or just people watching. It's a welcome break from the heat and good way to recharge batteries for the next hours of sightseeing.
Here is a little tutorial on how to make real Vietnamese Iced Coffee, my favourite.
Have a happy nice day, guys!