The actual Jumpseating in the US is not longer approved, unless you work for that same air line.
Pilot can request a jumpseat ride in another carrier and if granted, you have to seat in the back. If the flight is full and the J/Ss are open, sorry you won't go anywhere. ahh in other to do that you airline needs to have a J/S agreement with your airline.
It will be extremly hard (since Sept) to allow a jumpseater from a carrier other than a US ones that operates under 121 or 135 FAA Regulations. (I think CX is 129 (but not sure))
Interline tickets have to be purchased with your air airline and is usually a 90% discount of the coach full fare (Y code) since full fares are usually the same in every carrier once you have your ticket let's said a DL from ATL-LAX you maybe able to used the same paper to go with AA if DL is full.
ID 90's have the lowest priority so before you are granted a seat another employee from that airline or even a jumpseater from a different US Airline will have priority over you.
This information is correct as best of my knowledge, I used to commute for several years until I got the ax in Jan like many other pilots in the US.
Hope this help a little enjoy the commute,