Belize Free Zone
Entrance fee about 1USD
11km from the city off the Chetumal-Belize highway
Located by the border Belize Free Zone houses over three hundred stores. You can shop at many of the duty free stores for clothing, perfumes, liquors, and electronics. You can try your luck at any of the three casinos or eat in one of the many restaurants. No documents or passports should be needed as you will not go through Belize immigration, but take them with you anyways just be safe.
Finding other than Mexican products from Chetumal is not easy. As there are not much tourists, most of the stores actually sell stuff to the locals.