The US Gallon derives from "A pint's a pound, the world around!". A pint of water is 16 fluid ounces which weights 16 ounces - a pound. Two pints to a quart, 4 quarts (8 pints) to a gallon so a gallon weighs 8 pounds and is 128 ounces of liquid.
Close enough...
"A pint of clear water weighs a pound & a quarter" was what we learnt when I was a kid in Oz!
The US pint makes a bit more sense, as it relates weight & liquid measure on a 1:1 basis.
Our (& much of the rest of the world's) "44 gallon drums, are your "55 gallon", we were agreeably surprised when buying US cars, that the mpg figure was better than that we read in US reports.
It went the other way round, too--mpg figures from Oz & UK vehicle tests turned out to be worse (numerically) when tested in the USA.
Australia went metric in the 1970s, with few glitches.
By the way, your 1/2" & 9/16"AF spanners will do double duty as 13mm & 14mm spanners respectively.
There has been a certain amount of "re-Imperialisation by stealth" in recent years, with beer being sold in pints.(apparently it helps the little "trendoids" pretend they are in London)
Not all pints are equal, as some may be wimpy little US pints, & not full-blooded "hair on their chest" Brit pints.
Another thing is the revival of Whitworth threaded bolts, thanks largely to the massive output of these devices in India, which is largely unreconstructed "Imperial".