You can sprint using the Aux1 key.
Shallow water no longer instantly nullifies fall damage! Slime blocks are a good replacement. (or cloud armor, if you're fancy)
Leaves can be climbed up. This also makes them useful for breaking falls… as long as you don't hit a log underneath.
Slimes can steal your items. They will digest them after a few minutes.
The recipe book in the inventory is your friend. Click on an item twice to see what it's useful for.