I do keep used needles if they are not a problem since I change my needle each time I start a new project. I make a lot of totes and bags and used needles are perfect for the thick top stitching at the top of the bag...this seems to ruin needles so I take out my new needle and put one in that I have used already. This works for me. I store them in the empty plastic boxes that they came in and mark used on the box. Each time I put in a new needle I fill out a small form that I made which shows the date and type/size needle...I also sometimes stick the needle thru this paper slip when I take it out so that I know exactly when and how much this needle was used. Hope this helps someone.