Simply take a large dish, and fill it with liquid mercury.  Float things on the mercury.  Rocks, iron nails, witches, lead shot, you name it. It's best to start with the least ridiculously dense things, and build up to lead shot.

WARNING: Mercury is way bad for you, kids. Use appropriate caution.

I have students construct Lewis structures on the board starting at the noble gases and working backwards to the group 14 elements.  We talk about both second period then heavier elements.  As we move across the period we transition from molecular solids to extended solids.  

This is a nice transition from molecular chemistry to extended compounds.  I use this as a bridge into the solid state portion of the course because it allows me to review Lewis structures, trends in bond energies, and provide some descriptive chemistry information.