I usually cut a small chunk off and wrap some sellotape around the end.
It has to be enough to give a good representation of the colour & hair in that area.
An inch long would be ideal.
You can then staple them with a label or to a piece of paper or come up with some inventive idea of your own!
It doesn't really matter as long as its clear what each bit is.
All hair is dead, so I'm not sure what fresh hair is!