There are literally only 2 things that have to be brand new - the crib mattress and the car seat. Everything else can be second hand.
We have bought our swing secondhand, and are buying our travel system second hand this week. We were given our crib by a friend and we are reusing all DS' clothes, cloth nappies, blankets, etc. We have a baby monitor, baby gym and baby bouncer in the garage that we plan on reusing. We are getting rid of the high chair, but that is because we hate our one and would prefer a fold up one.
Oh, I am buying a new mattress for the basinett that comes with the travel system.
Besides car seats, I would avoid high chairs, stuffed animals, and cribs. There have been too many recalls on high chairs and cribs in recent years and I cannot keep track of which are not considered safe. With stuffed animals, you cannot easily wash most so it is hard to ensure that they are truly clean.
I have had good luck buying baby clothes at garage sales. I check for fabric content (100% cotton) and whether all the snaps are present. I also wash all clothes in a hot water and vinegar wash with heavy duty detergent then a second wash in cold water - baby wash to ensure that they are clean.
I've read not to buy a used crib. I think I would buy most other things used (excepting the obvious, like breast pump parts). I got a play mat for $4 last weekend and was super excited.
Besides car seats, I would avoid high chairs, stuffed animals, and cribs. There have been too many recalls on high chairs and cribs in recent years and I cannot keep track of which are not considered safe. With stuffed animals, you cannot easily wash most so it is hard to ensure that they are truly clean.
Re: Stuffed toys. Please don't buy any unless there is something special you want. People, especially those who have never had a kid, tend to buy your baby/child lots of these. DS has 3 garbage bags worth in the garage, plus an entire tub of them in his bedroom, I think we have bought maybe 5-10 of them in the 6 years he has been alive.
I sold my old carseats like instantly at my last GS. I was surprised how fast they went. I figured by the time this baby is a convertible it will be expired.
I personally would not buy stuffed animals or a breast pump.
But I think I would buy a crib it if was in good condition and there was a date still listed on it. Not a drop side or anything.
Car seat, crib (including mattress and sheets), RNP, high chairs, and anything the baby will suck on - teething toys, nipples if you get used bottles, pacis, etc.
I plan to hit a lot of garage sales/consignments and get mainly clothes. People will buy blankets anyway at showers. I did buy our stroller half off because it's in good shape. I also wouldn't mind getting some toys used like ones they can stand against and things like swing I plan to get used. They're so pricey and hit and miss if your baby will even enjoy them.
Diaper pail. I didn't want a pre-stinky pail. I'd sooner go without. I probably wouldn't do stuffed animals either.
I've bought a lot of used stuff, including items mentioned in this thread that others wouldn't. Used is the best way for us to get all the things we need or want her to have.
Really, anything with a motor or sanitization/safety standards. This is our first child, so if we "need" something I'd rather buy it new so I know how roughly it was used, when it was purchased, and have the warranty information on hand. Things like clothes or plastic playthings are fine on consignment. Anything we purchase now we're doing so with the idea that it will be used for subsequent children as well.