Buying second hand

My SO and I have agreed we're probably going to buy (most) of the baby stuff second hand. With the exception of a few special outfits, clothes in particular seem really silly to buy brand new.
I've drawn the line 100% against buying a crib, mattress, strollers or car seats second hand since I feel like that's a safety issue.
I was hoping for some input from some experienced moms though--is there anything else I should add to the absolutely MUST be bought new list?