Start buying diapers, wipes, rags, bottles and formula. Diapers should be bought in batches of progressively larger sizes. My wife started doing this immediately and when it came time for the baby to come, we already had nearly enough diapers to last us at least a year. This was also helped by diapers and other items being given as gifts by family and friends, but we never "expected" anyone to help, so we did it all ourselves.
Congrats! Words to live by, passed to me by a very wise man, "If you're somewhere you wouldn't want to run into your kids at when they come of age, you don't need to be there.".
But anyhow, I know the feeling and ain't nothing like it.
Congrats, just remember that they can pee 3 feet in .1 seconds if left uncovered (aiming is optional). Start buying diapers, you'll need more before its over.