Why are all of the items in my Singleplayer Minecraft world are gone?

I was on the same world about an hour ago and everything was fine, but now every item in my inventory, in my donkey's inventory (and the saddle), and every chest in my storage system is gone. All blocks that were placed are still intact, but any item that I had anywhere are now gone. Please tell me that I can get it back easily!
Btw, I just updated to the snapshot, that probably has something to do with it.