I talked to a lady seller on the street today. She said to me that she earned 25,000Vnd per day wandering around the old quarter, starting her day at 7am and ending it whenever she finished selling her stuff.
A little sweet, a little bit buttery, her produce was edible yams and sweet potatoes. Cakes and sweets can be made from them or they can be enjoyed as a simple snack. They are especially popular in the winter.
Cassava is another common food for Vietnamese who eat it mixed with rice or dipped in salt, sugar and chilli for their meals. This is not really something to eat everyday, but it's good on occasion. They are filling, can be eaten hot or cold and are sold all day long.