Allows for minecarts to pick up and put down certain block entities.

When a minecart passes by a chest, dropper, dispenser, shulker box, barrel, spawner, or tnt, it will pick it up. When triggered by an activator rail, it will attempt to place it back down again.

Minecarts with shulker boxes and barrels behave just like minecarts with chests, except that they will drop their items separately when broken. Shulker boxes will retain their colors and names while in minecarts.

Droppers, if they contain items, will drop an item on activation (they will only be ejected once they are empty). Future versions will allow dispensers to dispense items.

Instant Shulker box unloaders can be built by dispensing a shulker box next to a minecart and then breaking the minecart.

Requires no resource pack, despite the fact that the minecarts will visually carry their blocks!

What about hopper minecarts?
  Having minecarts be able to pick up and put down hoppers on their own would break many farms, and not be very useful. Hopper minecarts already have their own interaction with activator rails anyway.

Furnace minecarts?
  What are those?