Builder's Backpacks

This is a small, lightweight mod that adds a single item to the game:  The Builder's Backpack.

 

Found in creative under tools, or craftable using the following recipe:

 

This backpack will do a few things.

1. You can put blocks into it using the UI, opened by holding the item and sneak+right clicking on empty air.
2. If configured to do so, it will collect blocks you pick up into it, saving inventory space.
3. It will extend your reach by a configurable amount while you have it equipped.
4. It has a radial menu that you can open by holding the hotkey, default 'z' to quickly change between blocks.
5. While holding the backpack, right clicking it will place the currently selected block.