Medium in pill boxes... good idea. Oil paint in pill boxes... bad idea. (it doesn't prevent skinning over and drying)

However, I'm thinking about using slightly larger pill boxes for the oil paint and putting those little round felt pads on the underside of the pill box lids... then putting a tiny dab of clove oil on the pads.

Of course, could also simply put water in each box on top of the paint... but that's getting crazy and more work than screwing tops of tubes... though that would be a good idea to preserve small batches of mixed paint for further use. Those pill boxes are cheap enough to be throw aways when finished using.