Checkboxes to ranked list

Try this:

DynamicModule[{pos = Range[3]}, 
              Panel[Row[{Column[{"Controls", 
                                 CheckboxBar[Dynamic[pos],
                                             {1 -> "a", 2 -> "b", 3 -> "c"}, 
                                             Appearance -> "Vertical"]}], 
                         Column[{"Ranks", 
                                 Dynamic[Pane[ReplacePart[{0, 0, 0}, 
                                         Thread[pos ->
                                                Range[Length[pos]]]]]]}]}]]]

DynamicModule[{pos = Range[3]}, Panel @ Grid @ {{"Controls", "Ranks"},
    {CheckboxBar[Dynamic[pos], {1 -> "a", 2 -> "b", 3 -> "c"}, Appearance -> "Vertical"], 
     Dynamic @ Normal @ SparseArray[MapIndexed[# -> #2[[1]] &, pos], 3]}}]

Alternatively, using the second argument of Dynamic to update ranks,

DynamicModule[{pos = Range[3], ranks = Range[3]},
 Panel @ Grid @ {{"Controls", "Ranks"},
  {CheckboxBar[Dynamic[pos, 
      (pos = #; ranks = Normal@SparseArray[MapIndexed[# -> #2[[1]] &, #], 3]) &], 
     {1 -> "a", 2 -> "b", 3 -> "c"}, Appearance -> "Vertical"], Dynamic @ ranks}}]