My Starbucks Card
I seem to be able to make any Starbucks barrista’s day just by using my card:

Apparently, this is a fairly rare card and just seeing it brings a little bit of variety to their day. I’m happy to get a coffee and a smile each time I hand it over. I’ve used it in many different stores and it never fails to get a response. Amazing.

Comments
I get a similar result with my credit card, which I've covered in PowerPuff Girls stickers of MoJoJoJo the monkey -- people often think it's part of the card. It makes quite a few cashiers smile/comment. For me, having fun stickers on it makes using the card a little less painful!