New Post: How can I improve my PHPexcel File?

Take advantage of PHPExcel's fluent interface:

$objDrawing = new PHPExcel_Worksheet_Drawing();
$objDrawing->setName('')
    ->setDescription('')
    ->setPath('../../media/catalog/product/cache/1/thumbnail/75x75/9df78eab33525d08d6e5fb8d27136e95'.$_product->getThumbnail())
    ->setCoordinates('A'.$sum_total)
    ->setOffsetX(10)
    ->setOffsetY(10)
    ->setHeight(110)
    ->setWorksheet($objPHPExcel->getActiveSheet());

or

$objPHPExcel->getActiveSheet()->setCellValue('A7', 'IMAGE')
    ->setCellValue('B7', 'SKU');
    ->getActiveSheet()->setCellValue('C7', 'BRAND')
    ->getActiveSheet()->setCellValue('D7', 'GENDER')
    ->getActiveSheet()->setCellValue('E7', 'NAME')
    ->getActiveSheet()->setCellValue('F7', 'PRICE PER UNIT')
    ->getActiveSheet()->setCellValue('G7', 'RRP')
    ->getActiveSheet()->setCellValue('J7', 'TOTAL UNITS');

Avoid unnecessary duplication of nested method calls

$sheet = $objPHPExcel->getActiveSheet();
$sheet->setCellValue('A7', 'IMAGE');
$sheet->setCellValue('B7', 'SKU');
$sheet->setCellValue('C7', 'BRAND');
$sheet->setCellValue('D7', 'GENDER');
$sheet->setCellValue('E7', 'NAME');
$sheet->setCellValue('F7', 'PRICE PER UNIT');
$sheet->setCellValue('G7', 'RRP');
$sheet->setCellValue('J7', 'TOTAL UNITS');

Look at using the worksheet's fromArray() method

$data = array(
     'SKU', 'BRAND', 'GENDER', 'NAME', 'PRICE PER UNIT', 'RRP', 'TOTAL UNITS'
);
$objPHPExcel->getActiveSheet()->fromArray($data, NULL, 'A7');

Combine these techniques as appropriate