I don't know why I didn't think to make shrink plastic wine charms before, the very fact that they are illustrated means that they are perfectly suited for making matching sets. These are the first four sets that I've made but I plan on making loads more of them. The only thing I've yet to figure out is how to display them. I tried using a card for the button ones that I made but they don't do them any justice. I think I might get bracelet boxes to match the other ones that I got, it would make them more substantial.
I've listed them here in my etsy shop at €15 per set, I was in two minds about the price. Looking at other handmade charms on Etsy they are much more expensive, but I know I won't sell that many if I price them any higher. I'll have to see how they go and adjust accordingly.
Update: My bracelet boxes arrived sooner than I expected and they work perfectly. I'm much happier with them displayed like this and they would make a really nice gift for someone in this cute presentation box.