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inventory-plus
A Foundry VTT module to enhance the dnd5e inventory. Allows to customize your Inventory in various ways.
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SurveyJS
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try inventory+ with that you can add extra inventory category in your character sheet and set them up for example as a bag of holding (the bag accept only 500lb of stuff, weights 15lb itself but wont add the items weight to the character) or wathever you want.
For trading between players I would suggest Item Piles, its main feature is to make npc lootable and easily drag items on the map to make lootable piles but it adds also an usefull trade between players feature