I have the type of personality where I would MUCH rather be over-prepared. So we got tons of stuff beforehand. We also had 2 showers, which helped us a lot!
Prior to being licensed for 2 children with an age preference of infant to 4yo, we had the entire nursery set up (crib, changing table, twin bed, desk, books, diapers, diaper genie, crack machine, etc.). We also had 2 outfits and 2 sets of pajamas in every size NB to 5T, along with 1 pack of diapers in each size and underwear. This was a lifesaver since we used these clothes the first few days since we didn't have time to unpack and sort through all of their stuff.
We also had carseats (2 convertible Britax and 2 booster seats). Our county does provide vouchers for carseats, but we preferred to buy our own (that we'd get to keep) that we had time to research and not hope they would be in stock when we needed them.
We had simple toys (blocks, wooden train set, etc.) that we got from consignment sales and given to us from friends. We also had bottles, dishes, kiddie spoons, sippy cups, bibs, high chair, etc. And we had a meal for each baby food stage and always a box of Mac and Cheese!
I was way over-prepared, but I really liked that our first few days with the boys were spent together getting to know one another and not constantly at the store trying to buy all of the essentials. But I know others have said it would be hard emotionally to have all of the baby stuff in their home while they wait for "the call"- this didn't bother me but kept me excited that a baby (or two) would come since we had all of this stuff- they just had to!