During our regular game session, everyone keeps saying,"We need to find the mcguffin!". Is this a new sandwich or something?
A MacGuffin is a device, object, or abstract need whose finding or obtainment is the force that pushes characters and evildoers into action.
While MacGuffins is a typical plot device to push a story forward, in D&D is rather typical (I would say almost cliched) to use a broken MacGuffin, where the single pieces must be found and assembled. This allows you to carry long campaigns with different settings easily.
I strongly advise against the use of the so called Red Herrings (which are false MacGuffins that divert the attention from the actual plot/MacGuffin) in roleplaying. Players generally don't expect their attention to be diverted or the plot to be too intertwined. If they hunt a red herring and find out it is indeed a red herring, they could consider the DM wrong or accountable for having changed the story under their feet.