Hospital bag
A bag you already own is fine: roughly a weekend holdall. Packed by about 36 weeks and left by the door or in the car. Several guides split it in two, a small one for the delivery room and the rest for the stay, and a bag that later works as a changing bag earns its price twice. No official guide gives a size.
Childhome Mommy Bag: 115 €
Herschel Supply Herschel Novel Duffle - 43L: 120 €
Lässig Yula Weekender Changing Bag: 140 €