I have same setup as woods walker, with a twist.  I put  2" extruded foam in the base, made a mold that matched the diameter of the opening, filled the outside of the mold with "Great Stuff" and pulled the mold when the foam was set.  To this you can add plugs of extruded foam to separate items.
    If you carry frozen items this works very well.  Dry ice adds to the length of time things can be kept.  
    As an aside the barrel helps keep the fragile items safe.