Costco/ dollar store equivalent store in Spain

I’m getting married outside Barcelona. I’m going to be in town a few days before the festivities start and am hoping to purchase some items that don’t make sense to ship or fly with. I’m going to need a basket for the flower girl, baskets for the bathroom, paper bags for my welcome/ hotel bags and items like electrolyte packets water bottles and Advil to put in the bags.

Where would be the best place to buy bulk items? Has anyone ever purchased a different country Amazon prime to buy these types of items?