Note that if you plan having your already checked-in bag returned to you at AMS so these items can be inserted into that bag which is then re-checked, that it may not be possible to achieve this without payment of a fee. A bag is only short-checked to AMS if the onward flight is the next day or if there is a change of mode of transport at AMS (ie onward "flight" is by bus or train).
Remember also that if you check in a brand new, second (or subsequent) bag at AMS, you may have to pay a fee (depending on the free baggage allowance applying to your ticket, and any extra baggage allowance afforded by your status). Note also that any free baggage allowance you may have should be counted as the first bag and therefore you may find yourself already bumped up to the more expensive "second bag" fee for the first bag that becomes liable for a fee.