How much oxygen is put in say a 180-seater A319 or A320 aircraft?
An A320 carries oxygen generators for passengers and cabin crew, pressurized oxygen for flight crew (including observers) and some portable oxygen bottles [1].
I can't find the exact volume of the pressurized container, but it is pressurized to around 1800 psi (124 bar) when full; [2] (page 148) gives minimum pressure for flight and how long for it should suffice.
Average amount of air inhaled by an adult human is usually given around 2 000 l/h, which contains around 400 l of oxygen (at standard pressure). The passenger masks are required to last quarter an hour, so they need to provide oxygen that would have 100 l at standard pressure (but at 0.15–0.2 bar only) per passenger. Plus there are some (around quarter) extra masks for people who are walking in the aisle at the moment decompression occurs.
Only flight crew masks must be able to provide pure oxygen at sea level pressure to be able to keep smoke or fumes out in case those enter the cockpit. These are always supplied from a pressurized bottle, because it must be possible to turn them on and off as they may be used in other cases too (fumes, pilot feeling unwell, preemptively if the pilot is alone for some time etc.) and the chemical generator will release all their oxygen once triggered.