This is a bit of a clarifying reply.

First, I think you mean cask, not casket. Cask holds alcohol, casket a dead body.

Still, that's an insufficient explanation for the origin because, as with most units of measurements, they varied considerably from time to time. There are few (maybe none) units of measure that had a single value and then stuck with that. For the gallon, there was not one single gallon measure, but rather one used for wine, which is more or less equivalent to the modern US unit of measure, and one used for beer which was considerably larger. The former is the origin of the unit as used in the US, and the latter the origin of the unit as used in the UK and elsewhere. The US/wine gallon is the older term.

Still, that doesn't actually explain the origin, but instead just says "this is how it was used". The etymology of the word isn't fully known and may have just been lost to history if modern speculation is wrong (not that I can say it is or isn't). It's sort of like a folk etymology at this point.

Likewise with pound and ounce, we can address the history of the units, but that doesn't actually tell us something that it is based on. The Romans had a unit of measure called the libra, from which the "lbs" abbreviation originates, and that was in turn split into twelve units (ounces). The ounce measure was called uncia (oon-chi-ah) which is where the word "ounce" comes from. "Pound" (and also "pint", again as in beer) comes from Latin pondo meaning weight.

That same word uncia, which really means "one twelfth of [something]" is the origin of the English word "inch". This actually also calls into question your thumb-width meaning. An inch has always simply been one twelfth of a larger unit of measure, in this case a foot, and any connection to body parts is entirely folk etymology. The foot, however, can have such a connection and obviously "foot" means foot, but this is a unit of measure that also has been in use for ages and also has varied considerably from period to period. The Romans used the measure, as did the Greeks. It was called the foot and approximated that distance, but it wasn't necessarily based on the length of an individual person's foot.

All this to say, the origins you point out either don't actually address the origin, or else are simply ex post facto explanations, which also don't actually address origins.

So, tl;dr, these explanations aren't actually the explanations, and the exact origin of many of these units are less significantly encoded than their significance as conventions for convention's sake.

Someone else may know the exact instant that "foot" came into use in the ancient Mediterranean, and I hope they can. But I think it's at least worth addressing some of the assumptions that this is built on.