OK, I went and bought them for $15. He said he picked them up at a garage sale over the weekend, didn't know what they were.
From what I've been able to discern, this is probably a parts washer kit. Each of the cans has a colored dot on them near the spout (one black, one subdued mustard) probably to hold gas and/or kerosene The metal two piece clam shell type kit in the middle comes apart and holds rags, metal scraper, a couple different sized brushes and a couple cleaning brushes. All three hook together and lock into a metal pan. I looked it over pretty good and other than some scratches/surface rust this kit has never been used. The cans have never had anything in them.
Besides the word Kraftstoff 5 Liter on the can, there is a round symbol (see photo) with the letters TGL and numbers 4368 under it. On the side near the bottom is the word Feuergefahrlich. Kraftstoff means fuel. Feuergefahrlich means, flame risk or flame danger or something like that.
BTW, each can is 12" high x 9" wide x 4" thick. The cleaning kit thingy is 3" thick but the same other dimensions.
Anybody know anything more about these things?