About shirts, I tend to think a good quality T-shirt would sell better. I hate cheap t-shirts too, like the kind they sell 4 for $10 at souvenir stores over here. Labels should not just indicate the size, but some measurement of the thickness, like weight per square inch.
Another project I'm thinking of us auctioning some mementos on eBay, and advertise the auctions on my site. If that does well, it may lift my confidence for selling strategy cards or any kind of shirt.
How about a large upside-down basic strategy card on a shirt so you could just look down at it without having to twist your shirt all around? Or maybe a checkered one with the different rules (number of decks, s17/h17)? Funny but a little tacky perhaps.