Just my thoughts here, but I'm with Javan as well. For me, its hard to justify spending money merely to be someone else's advertising campaign. I can justify spending for function though. That being said, I personally don't wear 50/50, so to me theres no function in a shirt like that. Unless the shirt had a really kickass and original design, as opposed to just a brand's logo, I would't buy it.
That being said, I'm sure you can offer products that are both beneficial to your business, and functional to the user. Perhaps you can source some very lightweight visors? Just think about what products would benefit BPL members, tag it with your logo, and offer it at a reasonable price.