It'd be really nice if it were possible to combine partly-consumed multiple-use items of the same type into one. For instance, drag a 3/20 Random Kindness onto a 12/20 RK to combine them into a 15/20 RK, drag a 2/5 Fertilidust onto a 3/5 Fertilidust to give a 5/5 Fertilidust. Dragging a 3/5 Fertilidust onto another 3/5 just wouldn't work — "You can't combine those jars, they're too full."
A small expenditure of energy to merge them wouldn't be a deal-killer.