Tips although I did none of these since I’m a terrible shopper (my husband is worse) I really bought nothing. A gluwein mug or 2.
Pack another suitcase inside of a checked bag. Or bring an extra duffle. Bring bubble wrap and tape for ornaments.
Check and see if the things you want can be ordered in the states. I found lots that is readily available in the states, some of the stuff I liked was just as cheap in the US.
Enjoy the food and drinks! Wear waterproof boots and bring a warm coat. Hat and gloves. I was surprised how many were not prepared for the cold.