It turns out that the Silhouette is not designed to cut shrink plastic. I therefore cannot recommend that you do so, and I will not do so again. Nevertheless, that IS how I, with difficulty, made this bookmark. Next time I will print the design on the shrink plastic and cut a plain rectangle around it, using a hole punch to make holes at the corners.
After the plastic was shrinkified, using the directions on the package, I threaded 1/8 inch elastic through the holes and then tied the two ends together (not the neatest way of doing this, but I was on a tight timeline and had to make do with 1. what I had on hand and 2. my laziness).
Slip it around a book with the plastic on the outside and the elastic marking your page, and you have an easy go-to gift.
[I had this idea all by myself. After the bookmark was made, I saw this on pinterest, which takes the same approach of wrapping around a book with elastic.]