This mod is part of The Vanilla Experience.
A drag-and-drop mod which allows players to easily pick up and move minecarts without breaking them by holding right click.
You may also be interested in Move Boats.
mustSneakToPickUp (default = false): When enabled, will only pick up the minecart when the player is sneaking and holding right-click.
To pick up: Hold right-click while looking at the minecart. You can release the mouse button while moving the minecart.
To release: Either right-click the minecart again, or press the sneak button.
Here you can see a minecart being picked up; be careful with a tnt cart!