According to a list of "Jazz Age Slang" I found online (the 1920s are sometimes called 'the jazz age) 'noodle juice' does mean tea. I have no idea why though. The only thing I can think of is that in the Great Depression if people didn't have proper tea they might have to make do with soaking noodles in water and drinking that. This is just a guess. Don't know about Mrs Hoover either - the President during the first part of the Depression was Herbert Hoover so presumably it is a reference somehow. The makeshift tent towns that homeless people in the Depression lived in were colloquially called "Hoovervilles". OK.... On Wikipedia it says Mrs Hoover was prominent in the Girl Scouts and the Girl Scouts in America are famous for their cookies so perhaps they are going to K Street to get food donations from the Girl Scouts?

“Noodle juice and cookies with Mrs. Hoover. Whatcha think, for what? An ankle excursion.” It doesn't really matter what "Noodle juice and cookies" means. I accept Amanda's research as to their meaning. The actual sentence is a flippant answer, he could have said anything as the answer to the previous question "ready for what ?" was going to be obvious. That is highlighted by "Watcha think ? An ankle excursion". The two individuals must have a routine at that time to walk. And just for completeness "Watcha think ? is "What do you think ?" and "ankle excursion" is an unusual slang expression for walking.