Sorry, I know this is a weird request, but it's for a good cause!
I work with this group for people with learning disabilities in Cambridge. They're collecting the ring pulls from beer and fizzy drink cans for a special project, and are appealing for help. So if you have a couple of cans in your house or recycle bin, and wouldn't mind taking off the ring pulls and posting them in, it would really help. If you write "Mumsnet" somewhere on the envelope, we'll pile them all up and take a photo to show you all how many we get and what we're about to do with them.
I've heard that there may have been scams about collecting ring pulls in the past, but I can verify that this is the real deal. It will cost you a stamp, but if you can spare it the guys would really appreciate it. If you visit the page, there's an "About Us" section where you can see some of the group members and their work too!