It IS possible and I figured out how! I recommend doing this on your PC and NOT in the DnDBeyond app. Go into your character sheet and find manage inventory, then add a new item. Type in "component pouch," and add it to your inventory. It is under the categorization "container" and once added to your items will create a new tab under inventory next to "all," "equipment,' "backpack," and "attunement." Now you can click on that tab labeled "component pouch," check the box to add it to your "equipped items," and left-click on the name next to the aforementioned box. THIS will open up a tab to the right with a name, item description, weight , cost, and at the top a little pencil allowing you to change the name. I changed mine to "Snack Bag," and viola! Now I have an equipped item next to my backpack labeled "snack bag" which i can add all my homebrew snack items into, and its all neat and organized just like my backpack. Hope this helps!
Thanks to new updates, managing player inventory has become easier. You can add a backpack item, then customize it to suite your needs.
But what is the correct method for making a homebrew backpack item?
As of now you can't edit the extra space for a container only manage it in the sheet like that.
It is unfortunately not currently possible to make homebrewed containers, as per the Items & Equipment FAQ #5: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).
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It IS possible and I figured out how! I recommend doing this on your PC and NOT in the DnDBeyond app. Go into your character sheet and find manage inventory, then add a new item. Type in "component pouch," and add it to your inventory. It is under the categorization "container" and once added to your items will create a new tab under inventory next to "all," "equipment,' "backpack," and "attunement." Now you can click on that tab labeled "component pouch," check the box to add it to your "equipped items," and left-click on the name next to the aforementioned box. THIS will open up a tab to the right with a name, item description, weight , cost, and at the top a little pencil allowing you to change the name. I changed mine to "Snack Bag," and viola! Now I have an equipped item next to my backpack labeled "snack bag" which i can add all my homebrew snack items into, and its all neat and organized just like my backpack. Hope this helps!