There has been some previous discussion on this, and it depends on a number of factors:
how many endmills you have
how many different materials you cut
how much record-keeping you wish to (are willing to) do
I use a couple of different machines which complicates things, and haven’t really found a system which is a good fit.
Job shops usually segregate endmills by materials and usage, sometimes having complicated hierarchies encompassing categories such as:
a new endmill will be used for finishing passes in aluminum
a no longer new endmill will be used as an aluminum rougher
once worn it will be delegated to roughing in cast iron
I try for the much simpler:
used endmills are for roughing
newer endmills are for finishing passes (need to get a stock of HSS tooling for that)
unused are spares and will be put to work for finishing passes when an endmill is delegated to roughing
I am hoping to be more organized when my Nomad 3 and Pro arrive, and have set aside two small notebooks to serve as machine logs, and I’m going to source a set of colored markers and work up a color-coding scheme where each time an endmill is used the label on the case is marked in a color based on material and in a shape (or symbol or letter) which denotes toolpath.
See previous discussion on record-keeping:
which has a PDF.
To actually answer the question, mine are in plastic organizers: