When you go for dinner you will hand over your vouchers/cards to severs. You must tell them you have them. They will take them and bring back the wrist bands and put them on your right then and there.
this takes place if you have been in the park before 4 pm. If you are arriving after 4 pm, when you enter the MK they will place the wrist bands on you there.
I like to keep things as souveirns, so I prefere to come into the park after 4 pm as they gave the tickets back to us, but at LTT they took them. I will say that I did not ask if I could keep them.