Bagger is a very simple AddOn that opens all of a character's bags for player trades, as well as the Bank, Guild Bank, Auction House, Obliterum Forge, and the Scrapper, then closes the bags when the main task window is closed. Bagger was inspired by a defunct AddOn called bags_and_merchants by Elkano that existed several years ago. Blizzard negated the need for the primary functions of bags_and_merchants a few expansions ago when they built the feature to open all of a character's bags when interacting with the vendors in World of Warcraft. This AddOn is meant for those who use the original bag UI provided by World of Warcraft and who prefer to manually manage their inventory.
Note: This AddOn does not modify the bags, keep up with inventory, or automate equipment management in any way. Also, Bagger does not function to open bags at the mailbox, because I use the Postal AddOn and didn't bother with the redundancy.