I wasn't real sure about this either.

But I hadn't done the baby thing for seven years!
I can tell you what I had, and then ended up having to buy even more... (my baby was 6 lb 14 oz)
I had three packs of newborn
2 supermega packs size 1 (ended up buying a few more jumbo packs)
2 supermega packs of 2's (ended up buying countless more size 2 jumbo packs, and one case)
2 cases of 3's (plus seveal jumbo packs, and I've since purchased two more cases, since she's just made it to the 18 # mark!)
2 cases of 4's... I finally broke down and sold those to get the cases of 3's... since she's a little peanut.
Anyway... I knew there was one size that my babies were in for a long time, and I'm pretty sure it's the 3's... If I were you, I'd buy a couple cases of those, and a few more packs or one case of 2's... I don't know if you want any 4's or not? If you also want to stock up on those, I'd go easy--you may end up like me and not need them!