My best (stupid) guess is weapons. US gov has a ton of weapons. Already sells tons of weapons. Now the prices will always remain stable. Other countries would love to know that 30 million usd would always be able to buy an f15. Other countries declaring war will increase the value of the USD, as buying weapons from us government will decrease amount of money in circulation.
So the more money you have, the more freedom you have?..
I think it already works like that.
No, the more freedom America has, the more value American currency has. Our currency would be backed by freedom and eagle sounds, not the other way around.