my (@w, $c);
local ( $", $_ ) = ", ";
do {
  $_ = <DATA>;
  if ( defined $_ && !/^Product:/ ) {
    push @w,(split ' ')[0];
  }
  elsif ( @w ) {
    print "Product: ", ++$c, "\n@w\n";
    @w = ();
  }
} while ( defined $_ );
__DATA__
Product:
redball This is for Mike.
greenball This is for Dave.
Product:
smallbox This is for apples
bigbox This is for orange