You would buy shares of the associated index fund. Those shares would be the new ‘cash’
Of course, having a stockpile of any of the elements of that basket would also be a good idea as it would protect the buying power of your... wealth
If you can’t exchange dollars for the commodity basket or the basket for the dollars, how is it backed or convertible?
Actually, it sounds like a commodity based SDR. You wouldn’t “own” them. Rather, they would be to peg against which the dollar would float.