My characters can carry with them, everything they need to craft "X", what ever "X" might be.
They expend the consumable to do so, and "X" winds up weighing more than it's component parts.
Scrolls weigh more than the components used to scribe them;
Bottles of potion weigh more than the empty bottle plus the components for the potion did. (At least, if they are crafting a potion I *presume* they have a container for it. If not, the presence of the potion becomes truly confounding.)