"You've tried the cowboys now try the Indians" - there was a stall, at the Country Music Day we used to have in Harlow run by an Indian family selling clothes and so forth, which used to have a sign saying that.
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"Banjo" used to be rhyming slang for suit, as an alternative to "whistle" - "banjo and flute" or "whistle and flute".
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"Jerrybuilt" is a bit older than either of the Great Wars. It's in Brewer's Dictionary of Phrase and Fable, in the original 1893 edition - "unsubstantial - a 'jerry-builder' is a speculative builder who runs up cheap unsubstantial houses, using materials of the commonest kind".

And the suggestion in Brewer is that it is indeed related to the naval term "Jury Mast"- but this is said to be "a corruption of "joury mast"... ie a mast for the day" from the French word for day "jour".