A druid can shapechange into animal, and limited stuff changes together:
the clothing and one item held in each hand.
Can a backpack (preferrably loaded) count as an item held in one hand?
Assume the druid is strong enough in human form to lift several such backpacks.
Thing is, a backpack on the back is not a clothing item. So the DM has already ruled that the druid's backpack falls to the ground when they transform.
Druid's player then said he will take it off and hold the backpack in his hand when transforming, so the backpack transforms together with the druid.