Fish Oil

Fish Oil is a slimy substance dropped by various sea creatures. While it can be sold to merchants for a few coppers, its main purpose is as a reagent for the Shaman spell Water Walking.

Source
This item can be looted from most level 25-72 Humanoid monsters, mainly Murloc and Naga. With an easily-accommodated minor glyph which negates any need for this item, and an appropriately low sell prive, there's little point in higher-level characters picking this up.