<?php

$customerCount = 0;
try
{
    //configure the customer collection
    $collection = Mage::getResourceModel('customer/customer_collection')
    ->addAttributeToSelect('entity_id')
    ->addAttributeToSelect('firstname')
    ->addAttributeToSelect('lastname')
    ->addAttributeToSelect('email');

      //configure the order collection
    $ordercollection = Mage::getModel("sales/order")->getCollection();
    $ordercollection->getSelect()->join(
    'sales_flat_order_item',
    '`sales_flat_order_item`.order_id=`main_table`.entity_id',
        array(
              'skus' => new Zend_Db_Expr('group_concat(`sales_flat_order_item`.sku SEPARATOR ", ")')
             )
    )->group('main_table.customer_id');

    do
    {
         foreach ($collection as $customer)
         {
            foreach ($ordercollection as $data)
            {
             $product = $data->getSkus();
            }
            $customerArray = $customer->toArray();
            $customerREquiredArray['customer ID'] = $customerArray['entity_id'];
            $customerREquiredArray['First name'] = $customerArray['firstname'];
            $customerREquiredArray['Last name'] = $customerArray['lastname'];
            $customerREquiredArray['Email'] = $customerArray['email'];
            $customerREquiredArray['product'] = $product;
         }
    }
}