How to transport cargo using boats in minecraft?

Solution 1:

In a way, but it's a bit of a fuss.

Donkey and mules can have a chest right clicked onto them in order to give them an accessible inventory:

Image of a donkey's inventory

Adult donkeys can't enter a boat, but they can enter a boat as an baby, then grow up while still inside the boat. So, what you'll need to do is make a baby donkey enter a boat:

Image of baby donkey in boat

Then wait for it to grow up and add a chest to it:

Image of adult donkey in boat