Unless otherwise noted, you may only claim each offer once per user account / device / person / method of payment.
If it is allowed to claim an offer multiple times it will be clearly visible in the T&Cs on the product page. If that's the case you can simply buy the same product on offer multiple times and enjoy even more savings !
Please don't forget to repeat your cashback request depending on how many items you bought (if you bought 2 items you need to submit 2 requests)