[Rokuell]

Можно использовать список:

Код:

var
  L : TList;

procedure TForm1.FormCreate(Sender: TObject);
begin
 L := TList.Create;
 L.Add(ComboBox1);
 L.Add(ComboBox2);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
 L.Free;
end;

procedure TForm1.DrawIconFile;
var
  x: string;
  o, i, k, b, id: integer;
  cb:TComboBox;
begin
 for k:=0 to L.Count-1 do
  begin
   cb := (TObject(L.Items[k]) as TComboBox);
   cb.ItemIndex := 0;
   b := 0;
   o := 0;
   for i:=0 to cb.ItemsEx.Count-1 do
    begin
     id := cb.ItemIndex + b;
     x:=copy(cb.Items[id],length(cb.Items[id])-3,length(cb.Items[id]));
     if x = '.doc' then o := 3
     else if x = 'docx' then o := 0
     else if x = '.xls' then o := 2
     else if x = 'xlsx' then o := 1;
     cb.ItemsEx[id].ImageIndex := o;
     Inc(b);
    end;
  end;
end;