Mercado 27 de Octubre is Comalcalco's everyday market, useful for fruit, snacks, cheese, household goods, and a quick look at ordinary city life away from the ruins. It is not a grand historic market, but it is practical and local.
Come in the morning if you want the place at its liveliest. It is a good stop before heading out to the archaeological site or before catching transport back to Villahermosa.