Is it possible to add an option to sell items from your backpack? And/or "favorite/junk" label items so they do/do not show on the sell list? Reason behind the suggestion: after grinding through dungeons and the wild, lots of vendor items end up in backpacks and it is time consuming to move everything individually to the normal inventory, when the player just wants to sell the items.
You can drag&drop a backpack to a shop keeper and it will sell the contents of the backpack not the actual backpack. Just make sure to not have anything you don't want sold in the backpack.
Alternatively there is a find only spell named Etheralize, it's a mysticism spell that allows you to cast on a backpack which is engraved "ShopFood", it will instantly sell the contents of the backpack and the gold will appear in your inventory.
Hope this helps! Good luck!