In my sewing group, everyone keeps everything - the smallest off cuts, threads, odd sequins. They are kept lovingly in little treasure boxes to hunt through when you need something.
To fix onto a larger ground piece of cloth that you then embroider, you could use bonding fabric (something like this) - this would save your fingers 😁.
Oooh that sounds lovely, it must be nice to rummage through those boxes😊
Ahha yes, I haven't thought about the ironing-fabric-bonding fabric, that is a really good idea! I should give it a try!