As any machine sewist knows, you can't go anywhere without your seam ripper. But since said tool has a very sharp point (if yours doesn't any more, throw it out and buy a new one) it's a little tricky to transport it to workshops or other venues. My typical solution was to get an old wine cork and jam it on the sharp point before I put the ripper in my bag.
That works fine, and has the additional benefit of being no-cost. (If you need a cork, let me know and I'll be happy to send you three dozen or so.)
But when I taught a workshop last year, I was totally thrilled to be given a present: a new and improved seam ripper that protects itself (and you) when you're not using it.
Here's the ripper in defense mode: