Are they fungible? Do secondary markets exist? The whole promise of money is that you can just add and subtract the value of all those things to get a number in a reasonable range. With money you can meaningfully compare "a pound of gold" and "two pounds of silver," and you can settle a debt you owe Alice via a debt Bob owes you instead of keeping both imbalances forever.

Maybe this is me being broken by working in finance (even if just SRE for finance), but your example doesn't seem too far off from the problem of valuing ETFs or options or currencies or cattle futures (in theory, if you buy one and forget to sell it in time, some cows show up at your office...).