Depending on how many you have will depend on the best way to keep them. My first thought was a ziplock bag - then they are all together and you can see them easily and won't take up much room. I have lots of baskets and so use them a lot - and when Costco had a sale on those 15" x 15" plastic boxes (5 for under $20.00) I bought them and use them for UFO's. (Told myself I can't start another project until a box or basket is available.) My sister gave me 5 of those "shoe box" size plastic boxes and I have used them for holding scraps. I prefer to use things I can see what is inside.
Just look around your home and find something that fits.