IMHO. Not sure if I like the idea of trading... Its fine if you can, but if ship A and something Ship B needs and it is in excess of what Ship A needs, then make it available!
But also,never give up something that is aboard the boat, regardless of whether it is on the tour path or not! Again, IMHO.
Russ Booth (Rich's mentor and mine, and the guy who wrote the book on sub restoration) so badly wanted some of our torpedo tie down straps (he had none and we have a full set)... and as much as I loved Russ (my "big brother" as I like to think of him) I had to say no. If I had more than a full set, then it would have been different.
We make stuff in excess available... if it is in any way a consumable (glass light fixtures, or dishes for instance) we try to have 200% of what was there. The rest is trading (or actually GIFTING) material.
Karl Marx Rules!!!
PF