I'm not sure I follow, what are the reserves? If we are talking about the entire economy as an actor, a number in some magnetic tape can't be. Neither can be food or infrastructure unless it is properly preserved. So my guess is that the right reserve would be a people. People that aren't adding value today, are excess capacity that can be used during bad times. Guaranteed income is one way of maintaining that extra capacity.

Also, I'm not sure that anthropomorphizing the economy, while interesting, is the right level to think about this.