Bubbly elevators have been around for a long time, but they haven't been the easiest to build. This tutorial makes it easy and complete.
Armour wardrobes are a cool addition to show off red stone skills to all of your friends. If you have a wide variety of gear this makes it automatic for switching.
Inventories can get congested quickly with rotten flesh and dirt blocks. with a trash can you can throw out unwanted objects to help clear your inventory.
Piston doors are great for builds that are meant to be secret, to open the door you have to know where to go. So if your wanting to hide from friends this is a great suggestion.