Today I'll show you how to LOCK A CHEST WITHOUT MODS!!!! It's quite simple. (and no, not cats sitting on chests, although that's also a nice way to lock chests) All you'll need is four blocks of something that's not transparent, i.e glass, tnt, glowstone. PS. You have to have cheats enabled. What you'll do is this:

1. Stand where you want your chest

2. Surround you with your blocks.

3. Do this command /setblock ~ ~ ~ chest

4. Do this command /blockdata ~ ~ ~ {Lock:Chest Key}

5. Rename anything to "Chest Key"

6. Right click with your bare hand, and it'll say "Chest is locked!"

7. Right click with the key, and you can open it.

It'll also work with large chests. Just place an ordinary chest beside it.
I used the name "Chest Key" but you can use whatever! For my resturant, I used that for my chest to store my money. Have fun using this!! ~Wolfy