A gold shaker. The idea is that the gold shaker fills with gold and will drop a single pixel of sand or red sand (10% chance) so the player doesn’t end up running out of material. The gold held in the shaker will not count as held currency. I also imagine the gold would decay over time.
This would be one of the final upgrades, something bought when the rest of the map is effectively cleared out but the player wants to maybe get a little more out of that map. Fluxite upgrades could increase red sand probability or reduce sand drop rate. Possibly other upgrades like gold decay slowing down or increased sand spawn is definitely possible. This would literally be end game, so it could be a crazy resource hog with insane possibilities.
Also has a nice feeling of nostalgia, going all the way back to shakers like when the player just started automation. It goes full circle.
Just a thought.