With Openables you get a button appearing automagically when you loot any container.
Left-Click on the button loots the container and loads the next one until all containers in your inventory have been opened.

Features

Apart from all the generic containers (boxes, lockboxes, satchels, giftwraps etc) special containers are also supported

Clams
Geodes
Tome of Valor (never again lose valor because you already have a unique container in your bags)
Valorous Commendations
... and many more

Open-able detection is done in a locale-independent way so it should work in all client locales.
If you come across a container that is not supported post a ticket and it will be added promptly.

If ElvUI is installed the Openables button will skin itself to match the theme

v1.x -> v2.x Notice

If you are upgrading from a v1.x ElvUI_Openables remove the old folder, the addon name has changed.
It will nag you if you load the game with both but best if you proactively remove the previous version.

Usage

When the addon is first installed the magic button will appear at the center of the screen.
Alt-Click and drag to move it to your desired location. It will then disappear until you need it.
Click it when it finds a container to open it and loot the contents.