That was my original goal, that you could build up a playlist by putting a bunch of tags into a dish or container of some sort.
Sadly none of the hobby RFID readers support more than one tag at a time, they don't pick up anything at all if two tags are within the field.
You could have multiple RFID readers hooked up and have a tray with multiple slots sufficiently far apart and do it that way, but the readers are a bit too expensive to go that route.
Guess we have to wait for that particular tech to cheapen up a bit.