I was thinking that it might be best to group similar types together, as close to the Linnaean taxonomy as possible. I would have originally said to just use the classes under phylum Chordata, but ... we have invertebrate monsters like slimes and, well, arache, not to mention all the mythological creatures and the undead ones.

[he labels each bag with the contents and the date: you can take a scientist out of the lab but he will always designate his specimens]