I keep the empty needle boxes when they've been used, and if I've only lightly used a needle, I put it into the relevant slot in an empty box, but put a blob of nail varnish on the box so I know it doesn't have new needles in it. If a needle has had heavier use however, I drop it loose into my box of feet, accessories etc. Then if I need a needle for some less than high standard (!) task (e.g. I am about to shorten my garden parasol cover to fit), I can use one of those.