I used 3 in the first couple of hours with my first...
Meconium, inept nappy changes, baby posseting up my blood she'd swallowed on the way out....
DC2 caught me out because you have to be way more aware of positioning during nappy changes for boys - make sure penis is pointing straight down in the nappy! So got through loads with him.
Also bring more pants/dark coloured bottoms than you could possibly anticipate for yourself...