be aware that you can ONLY put a bag in another bag or a box if it is empty.
You can not take a bag full of stuff and place it in another bag or box.
Beyond that it's simple drag and drop - and if you are out of empty slots in your bank try your house vault - even a 5s per week single room starter apartment at the local inn gets two house vault slots. In a pinch you could also stash the bag in one of your broker slots and just not set any sell prices.