toastie, the mechanics of making these are actually pretty simple--you need cardstock for the "holders" and cardstock for the "passes"--each "holder" is an 8.5x11 sheet folded up and glued in thirds with a diagonal slit to put the passes in (see my photos).
The "passes" are each 1/3rd of an 8.5x11 sheet--like I mentioned I modified a template I found on theknot. I used a corner rounder to get the rounded corners but you could use scissors as well.
To get them to come out right just takes a bit of experimenting with your printer (i.e. lining everything up), ink, stamps...good luck!