I was thinking rear quarters (inner and outer), boot floor, rear panel, slam panel, crash bars etc.
Why? The only realistic way to keep all of that is if you cut the whole back of the car off in the rear door shuts. Removing the quarters or rear panel from the boot floor effectively means sacrificing one of them. The only reason I can see for keeping any of that it is to repair crash damage. And who is going to do that to an Omega these days?
It's just a load of work to get a bulky pile of bits you're never going to use.
Much the same applies to all the other junk that's often suggested you keep
just in case: just because you can, doesn't mean it's worth doing. And there is absolutely no point in keeping parts that are readily available new, so brakes, wishbones, struts etc should stay on the scrapper and keep it rolling.
I say this having done it all in the past, and it's a huge waste of time, effort and money. Keeping this stuff is
expensive, especially when you eventually chuck it away after 10 years....
I
would walk around the donor and keepers and swap the best bits over, like the lights mentioned. But the worse parts would go in the Omega shaped bin.