I have just checked my stock for my HO scale US layout and it makes worrying reading when you know that the layout is just 8 feet by 1 foot!
2 Steam Locomotives
15 Diesel Locomotives
10 Passenger Cars
73 Freight Cars (40 box cars, 19 hoppers, 3 tankers, 4 flats, 4 caboose, 1 crane and 1 boom car)
I think I may have bought rather too much!