One inventory slot can hold a whole harvest
Stardew Valley treats a backpack as a grid of item slots, not as a container with realistic weight or volume. Identical items can be grouped into a stack, so pumpkins from different harvests can accumulate in a single slot instead of taking up one space each. A stack can hold as many as 999 pumpkins.
That distinction makes the farmer’s carrying capacity depend more on how many kinds of things they’re hauling than on how much produce they have. A few hundred pumpkins may occupy one slot; a mix of crops, tools, and materials uses more of the limited grid.
A practical shortcut, not a physics simulation
This system keeps routine farm work manageable. Players can gather a large crop, carry it back to the farm, and sell or store it without making repeated trips simply because the harvest is bulky. Expanding the backpack adds more slots, while stacking lets each slot represent a much larger quantity of a common item.
The result is a useful bit of game abstraction: the farmer can be overloaded with variety, but not with hundreds of identical pumpkins.
