As well as their museum at Covent Garden, the London Transport Museum have a large depot at Acton where the majority of their collection is stored. I went to one of their occasional open days.
They have many more vehicles than they can display at the museum: I had a look round the poster store, where they have publicity posters going back over a hundred years:
There is an amazing collection of signs: Signalling and power control equipment: And, finally, a small piece of the spiral escalator which was installed at Holloway Road station in 1907, but never worked reliably/safely enough to go into public service:
It was a struggle but I resisted the temptation to add a couple of A-stock luggage racks to my own collection. They were selling quite well: