You can buy from them and also go to school. What is prohibited is for you to participate in such events.

I live in Canada and Halloween is approaching. People here are starting to decorate their buildings with Halloween theme decorations. My school is starting to decorate and the shop i buy food from are decorating as well. I hate Halloween and i never participate in it. But am i sinful if i shop in a place that is decorated? What about when i go to school? .