I love whenever you tell someone or someone tells you that you are going to back up while they are out- "Hey I won't have anything for you to worry about" and then Murphy's Law hits!
The oddest things will occur during your watch or just then an onslaught of crap begins to hit you that makes it harder for you to get your own work taken care of. Oh the life of backing someone up. It happens way to many times. You just never know what will happen when you are backing someone up.
Good luck and remember don't say "It should be pretty slow" to that person backing you up.