Interesting thing I found when attempting to deploy rockets the other day. They are classed as weapons, not payload.
I have re-assigned all CFS3 commands to joystick, throttle buttons, and assumed that the Select Payload would refer to Bombs and Rockets, but it does not. It refers to Bombs only.
However both Bombs and Rockets are classed as Weapons, so I changed my joystick command from Select Payload to Select Weapons, and can now cycle through all the Ordnance with this one button.
The Fire/Drop Ordnance key now drops whatever is selected.

The only difference between deploying Internal Weapons/Payload/Ordnance like Bombs and External Weapons like Rockets is that the Internal Weapon requires the Bomb Bay doors opening first. Otherwise, you select with the same key and drop with the same key.

It would have been nice if they'd mentioned this in the Help file or Manual, or something.

Thanks for clearing that up.

But like I said, it would have been nice if this was explained in the manuals somewhere.