One of my favorite things to get at the Mercado are these vegetable bags. They are little bags of veggies already cut and ready to cook with. They are only Q 1 and work well with almost any dish. It's nice when you want something quick and easy, especially when you are lacking in kitchen supplies.
The Mercado is the place to go if you want something for a decent price. It's the mall of Guatemala and is always an adventure.