Party or dinner should be consider.
But if the budget is limited, I think most people will be happy to pay by themselves.
For Banner, Snack/Coffee and tour, local people can give their recommendation and the estimated cost.
For T-shirt, we can launch a T-shirt design competition in GNOME community. The winner will get a special gift from Korean. This is just an idea, if everyone is agree, we can think about the gift and detail to work on this. This competition will also help to promote and marketing GNOME.Asia 2013.