Best containers to store oil based ink?

we use tin cans from house of cans

http://www.houseofcans.com/seamless-10-oz.-3-1/8-x-2-1/4-p-1855-l-en.htm...

What about small mason jars? Maybe small paint cans?

Avoid plastic containers. Oil-base inks can oxidise through the plastic, forming a skin all around, not just on top.
Personally, I put small ink mixes in used 6-oz. pet food cans; open the lids with a can opener rather than the pull-tab, and there won’t be a lip to interfere with the ink knife. No lid this way, but you can cut ink covers from photopolymer plate cover sheets (I also use orange vinyl stripping base) or just let the ink skin over.
Larger mixes I put into clean used ink cans.

I use old Manila envelopes coated with a silicone spray. You can write the name on the outside with a grease pencil, and can be stored in a filling cabinet or a shoebox with the lid on the bottom to absorb any spillage.