AdventureBackpacks won't immediately stack its contents to nearby chests unless the user first brings items from the backpack into their main inventory, so having this functionality would be a nice bonus. Custom containers aren't currently supported, but one can dream.
However, there is a workaround to improve the workflow, by changing two config settings:
QuickStackHotkeyBehaviorWhenContainerOpen = QuickStackToBoth
(default: QuickStackOnlyToCurrentContainer) - Recommended. This allows the Quickstack hotkey (P key) to work even while the backpack is open, otherwise you need to close your inventory and then press P in order to get it to work.
and optionally,
DisplayQuickStackButtons = Both
(default: BothButDependingOnContext) - Optional. This makes the small "Q" button appear which will also stack items from the default inventory into nearby chests.
So the current best-case scenario workflow is, once you get back to base full of loot in inventory and backpack:
- Press P to quickstack from inventory to nearby chests
- Press i to open inventory
- Press "Take all" button on backpack to move items from backpack to inventory
- Press P again (or click the little "Q" button if you optionally enabled it)