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)