Whoops. Forgot a parentheses. Take a look at the corrected version below. (corrected the version above too… in case anyone else tries to use it)
foreach($_SESSION['cartthrob']['coupon_codes'] as $key=>$item)
//this is the coupon code
From the above, it sounds like you can use multiple coupons if you order multiple items. In my tests, even when I order multiple products, only one coupon is applied.
Can multiple coupons be used on one order?