Like X mentioned, we ran an Amazon Associates webshop for some time - basically it's a page hosted by Amazon and configured by us to match the site's theme, and we set which products are listed - Amazon does everything, we get a comission (which was IIRC between 5% and 15% or thereabouts? IIRC we earned about $80 from it over time, which was pretty much without us maintaining it or keeping it updated much).
I think continuing with that - referral links or shops to Amazon or similar parties - would be the safe option. That way, we're basically just advertisers for those stores - and they get to deal with all the legal repercussions.
Amazon will work fine for the games and part of the merchandise, IMHO. If we integrate it into the front page and preferably make it relevant to the articles, that would be a double bonus. I do think it should be discussed with donators though; technically it's ads, and the donator promise is that you don't get ads. We could also just make it a user-configurable setting, that way we'd get guests and whoever didn't turn it off to still get us some commission.
As for things like custom T-shirts, I'm sure there's a similar service for that too; I'm not going to order shirts and have them delivered to my house for re-shipping, that's probably going to inflate the price far too much
. It would mean we'd only get a few percent in commission, but at the same time if members of TLS would sell their designs via a site like that, they would get a bit of money too.
I'd like to add "Everybody wins", but in reality, only the stores themselves and the management and shareholders there would,
. [/cynical]