The UK show How Clean Is Your House is chock-full of useful tips, including this doozy:
For use in empty refrigerators/freezers—good for when you are moving out. The ladies filled a normal baking tin with unlit, plain (with no fuel or other products added) charcoal briquets and let them sit in the fridge with the door closed. The porous property of the charcoal will absorb the odors.
For those whose housekeeping habits are, shall we say, mellow, this is a good one to remember.