I was planning to ask gog support to turn them into gift codes (since I haven't downloaded them), but someone said he tried and support refused for some reason. I'll probably try anyway later.
I'm not very sure if I'd trade them or simply give them away to someone who's interested either.
Crap, really? I was planning on gifting some stuff if I crit'd it too.
But you can choose to get gift codes right there and then, once you get a critical hit. It's the way I do it, since I would feel a little weird writing to support - "hey, thx for the gift, but, I really don't want it." It works also for games you do not yet own, so it's the easiest way to go ;)