Yes. This is common question, particularly in instances where there is a minimum order value to qualify for free shipping. You can and should redeem multiple promotions, purchasing them in a single checkout session.
In this case you will likely have 1 order number for multiple redemptions, that is fine. You can enter that order number for all redemptions.
Just be sure to check closely since Amazon and other marketplaces sometimes assign multiple order numbers, even when all items are purchased in a single checkout session.