I've whipped up a Winter-een-mas crown that you can print out, cut out, and then tape together.
The first image is the front and back, and the second image is an additional plain piece that you can cut up for inserts on the side to adjust the overall size of the crown. You know, for you fatheads out there.
Image 1 (Front and Back Pieces)
Image 2 (Adjustment Strip)
I recommend using a heavier paper weight for the crown than just standard printer paper. Or if you use printer paper, after you print it out stick the page between two books, so that it dries nice and flat. Then just cut along the edges and assemble to fit your head.
The adjustment piece can be cut up and inserted on the sides, a plain strip if only a small adjustment is needed, or a strip with a spike if a larger expansion is needed.
Enjoy, and post some pictures!