Too many great responses to read them all, but I will echo the big one for us - Don’t buy anything new if you avoid it. Babies grow quick and family members LOVE to give gifts to babies. Used stuff is invariably just like new.
Some things are tough to buy used because of safety. Car seats, strollers and cribs should probably be bought new as they need to be safe. Everything else, buy used.
This reminded me of yet another thing. I have a friend whose daughter is about a year older than my daughter. When her kid was 2, and my kid was 1, my friend mentioned, ruefully, that she had a garage full of infant stuff that she wished she could find someone to give it to. Not in so many words, but I sort of implied “um, why didn’t you give it to ME?” and her answer, which made sense when I thought about it, was that she wasn’t sure if people would be offended if she offered them used things, because some parents feel very strongly about having everything for babies be new. So I would recommend that if you are open to receiving second-hand things, that you pleasantly make that very clear to people you know with older children.