I didn't feel underpacked at my hospital birth at all but she was born at 5:33 am and we stayed until 2:00pm the NEXT afternoon (so we spent one night in the hospital). The day we spent there was filled with getting the hearing test and having her weighed ,etc. Even when DH went home for 5 or 6 hours, I was learning how to nurse and holding my baby. That said, I remember packing:
Clothes to go home in
Pillows to sleep with
wool socks (someone said hospitals were always cold)
Baby clothes to go home (we just used the t-shirt and blankets the hospital provided while there).
I didn't pack anything for entertainment at all (though now my laptop might go).
Underwear (but now I'd probably pack depends)
I did wish for an extra pair of Mesh panties while I was there so I might consider order a pair or two of those since the hospital only provided one which was immediately soaked in blood.
In short, I packed light and didn't regret it.