No good luck pieces for me - don't believe in it, but that is a different topic I won't get into. Momentos, not really - the only thing I'd take is pictures of the family, but they travel with me (me and wife on tandem and two little boys in a trailer, thus tandem4rider).
Have I seen anything? You bet. To each their own, though. I don't see the need to ride with a boa wrapped around my neck, but if another chap does - that's his business and doesn't affect me in the slightest. Goes for everything else I've seen or heard of as well.
Carrying something of your own is one thing, being asked, as David from Boise has suggested - that is a bit weird (for me), but again that is your business not mine.
Whatever you carry, enjoy the ride.