I've never really thought about doing something like that. Without publishing new content, it feels uncomfortable to take in more money than we raise just now. The ads, current level of subscriptions and my contribution cover the bills pretty much perfectly, so there's no real need for more site income at the moment.
That said, if there's untapped demand for something like a t-shirt (which would be awesome, I agree), I could put that together. The income could just sit there for a rainy day. Will investigate costs and think about a design.