Storing rice krispie treats
I don't know about the safety standpoint, but from a texture standpoint -- don't refrigerate them.

The problem is that they turn into an brick when cold -- rather than being a nice dessert, it's something that you have to gnaw at and fear that you're going to chip a tooth.  

You might be able to get around this by warming them back up before serving, but I'm not sure what the best way to do that would be.  (microwave?  low oven?)