I've talked about "the gift shop" a lot, sometimes in remote locations, high in the Himalayas maybe, in some national park. T-shirts would likely be specific to the region, with some mix of franchise motifs, e.g. Athena and pirates.
Given our brand of esoterica on the flats though, very spatio-geometric, it's the geometry toyz, ala Math 'n Stuff near Seattle, that really give us away as CSN. This presumes something about our clientele: they're philosophical, in the sense that geometry and philosophy have an historic alliance (like, read up on Neoplatonism if wanting to know more).
When you cross geometry with T-shirts, you get M.C. Escher, perhaps also on placemats. Your management has options who to buy from. Some don't stock T-shirts in wild abundance.
So how does the gift shop work with the games? On nearby Belmont we have Avalon, which gives a sense of the setup. Patrons buy an internal currency and their rewards come from behind the counter, based on success at the various games.
Greenpeace might set a business rule that when a patron scores a total of $50 towards that NGO, a free T-shirt gets triggered, perhaps from a catalog selection (visible on-line). Duplicate this arrangement another hundred times and you see where games might promote the flow of souvenir goods.
Given this is a geeks' circus, there's lots of attention to security, in the sense that a child working hard to help the polar bears, wants to know how this funding is used. Strong fund accounting on the business end is what gives patrons the sense of satisfaction, versus a bitter taste, when winning big for the cause.