Aside from small convenience and souvenir stores, there's not much shopping to be done in La Pesca. There's sometimes a small market in the first north-south street just past the canal bridge coming into town, but it's much smaller than what you might be used to from bigger Mexican cities and it'll be mostly closed down by the afternoon.
Be sure to bring as much cash as you'll need for your stay in La Pesca, because there are no ATMs in town. A handful of stores and hotels will accept credit cards, but most will not. However, there is a PeMex station just west of the canal bridge on the west end of town if you need gas.
