Keen for them all to be friends again, he agreed (DH20)
See steak and kidney pie.
"You can kip under that" (PS4)
"He wants a kip, and his bar's turned into a railway station." (DH29)
An ice cream dessert (a sundae) served in a tall glass, and consisting of layers of chopped fruit and ice cream in layers, with whipped cream on top. The dessert is eaten with a thin, long-handled spoon. It's possible that 'Knickerbocker' refers to the shape of the glass, which looks rather like the leg of a pair of knickerbockers.
They ate in the zoo restaurant, and when Dudley had a tantrum because his knickerbocker glory didn't have enough ice cream on top, Uncle Vernon bought him another one and Harry was allowed to finish the first. (PS2).
Loose-fitting pants gathered at the knee or calf. Knickerbocker was a nickname for the early Dutch settlers in New Amsterdam (present day New York), who used to wear these fairly racy trousers. Related: New York Knicks, knickers. See also plus-fours.
Play on words: "Night Bus," buses which run in London during the night. See full essay. Also suggests the concept of "knight in shining armour" coming to the rescue of a person in need, in this case a stranded witch or wizard.