Gift Buying Can Be Tricky

Buying gifts for people can be hard, especially if you receive one unexpectedly.  When this happens, what do you?  Should you buy one in return? This seems to happen every year where you have your list of people you need to buy for, but then that extra gift turns up.  The person you didn't expect to buy a gift for buys you something and then you debate if you're going to go out and get something for them.  The person probably doesn't expect a gift in return, but should you buy something anyway?

There could be a co-worker who buys something for everyone at the office, or a friend who buys something who normally wouldn't.  Would you go out and buy something in return?  What would be the right thing to do?