Might I suggest a little Key symbol on the top right or left corner for Key items to make them easier for players to find in their item stack and remember that they can only have one.
Hi! Just wanted to let you know, that I finally found some time to upload the first draft of the cards. Hopefully will find some time later that week to add the key-symbol and templates you asked for later on: https://prismaticnoiseproject.itch.io/weapon-armor-cards-runecairn-wardensaga