what to carry

[Mortblanc]

As for spare parts???

We have a saying over here; "two is ne and one is none".

It is not exactly true but let's look at the OP.

We are dealing with TWO Greeners and I am assuming they are identical.

A Greener is two separate single shot firearms attached together! The op has two of them and therefore has 4 separate shotgun actions.

Should one side of a Greener break the other side is still operable, and the OP still has three shooting platforms.

If the same side of each gun breaks he still has two single shot platforms.

If opposite sides of each of the guns breaks parts can be cannibalized and he still has one DB gun. (and in that case if different parts are broken a swap and repair could make one side operable and three actions again usable)

This is after he uses the Greener for the thousands of shots one would expect from such a firearm. I personally know of Greeners here in the states that are 100 years old and still going strong.

I can see two identical double barrel guns lasting several lifetimes.
That design was developed in an era when bird shooting meant hundreds of rounds would be fired over a weekend. They are built like very elegant tanks.