No one really want to go out shopping if they can just buy the same exact things online and even at a cheaper prices. Show him the discounts that you are saving at websites like Groupons with the weekly and holiday discounts.
Also compare prices and take him to stores and show him how much these items cost in stores. Once he realizes you are actually saving money by shopping online, it will probably convince him this would be a good idea. However, try not to get carried away shopping online.