Surely every craftsperson has one of these! If not ~ start now!
First find your box. A small tin will last for several generations ~ that is the usefulness timescale that should be anticipated.
If salvaging a pile of matching buttons ~ matching style and matching size ~ then take the time to pass a thread through them all. This will cost a few minutes of your time now, and will save thirty minutes of someone else's time later. A good investment. I was reminded to write this note when preparing the page on recycling a shirt [114425].
Grandchildren of the right age are good at sorting button boxes! Maybe it would be a good exercise at learning to count ~ How many red ones?