For last year's event I made some cassette tape sugar cookies. I was excited about the concept, and was actually pretty happy with the outcome at the time.
You can see that I was still learning about royal icing consistency....those looked a little melty!
I used a standard, no fail sugar cookie recipe, which you can find here.
I have finally figured out what works best for me in terms of royal icing. I basically use the recipe in the post linked to above, but with a few changes. Instead of 2.25 lbs of confectioners sugar, I use a 2 lb bag. Also, I use the whisk attachment instead of the paddle on my stand mixer, and let it run on low for about 10 minutes.
I use the icing as is for thicker piping icing. Then I use a spray bottle to dilute the icing for flooding. I found this tip on several baking blogs, but the original posting seems to have come from here. I'm glad I finally gave it a shot!