For the annual Penguicon event in 2016, I designed custom hotel door key cards for our attendees.
They hadn't experienced this particular kind of keepsake, and the cards ended up being so popular that the front desk was handing out blank keycards as souvenirs to attendees who didn't have rooms at the event.
This was made possible by a sponsorship I cultivated with Liquidweb Hosting, who provided their logo and otherwise allowed us to do whatever we liked.
After forming relationships with several providers of a service like this, we went with the one that provided full color at the best price for our quantity.
At the same time, I created privacy door hangers for the attendees based on a Dr Who concept.
I also designed a Star Wars concept hanger and a Lord of the Rings hanger, though we decided to go with Dr Who after testing.