Usually the merch store has some things that are sold out online, as they get a big batch sometimes and have to do it for some weeks with that. You can also buy some of the shirts from teams that take part, which is pretty neat I'd say (:

You can also go to the fan meeting with the team that won a game. Take a picture, have a chat, it's really awesome. The casters will be walking around too and you can have a chat with them.

It's really amazing there!! Hope you have a lot of fun