Cool could this pick up from other units that have resources and drop into other units maybe allied units too. Also there should be flag so it can't pick up for workers (or can only pick up for workers -for units that carries resources for workers, that would be interesting, like the ox in Stronghold lol)
Maybe flags for whether they can deliver to allied units and other controls like that.
Basically harvesting other units (not map units) and delivering to other units, what it can harvest and whether it can deliver to should be stated in a list and whether it can deliver to or pick up from allies. Units that store resources would need a flag to tell other factions that they can only deliver to them too.