What is the meaning of "having one's kitten in one's pocket"?

Solution 1:

To have a kitten in (one's) pocket is not an idiom in English. The idea of repressed or controlled anger is only a guess.

Almost all the results from a Google search referenced that passage or instances when someone actually had a kitten in a pocket.

How seriously would you doubt the abilities of a man who was so capable that he came "back from Dunkirk with all his equipment correct and accounted for and his kitten (safe and calm) in his pocket."

Solution 2:

Couldn't it just be a metaphor? It can be inferred that Dunkirk was a harsh place. Corporal Turnbull had returned from it safe and sound, and even the metaphorical kitten in his pocket had not been harmed.

Solution 3:

According to Chambers Dictionary of Slang, a 'kitten' can be (or was) 'a pint or half-pint pot' (19C). A small 'cat' (cup).

Perhaps he returned with all his equipment correct and accounted for and his beer glass still in his pocket.