The Diaper Bag has pockets on the outside for things that are needed quickly and often. The roomy inside stores things that require more room or are not needed as often.
The shoulder strap makes it easy to carry the bag. If it had handles, it would require one hand to carry it. The strap leaves hands free to carry the neonates® doll.
A Diaper Bag should be carried whenever you leave home with a newborn. Important things to pack are:
clean diapers (and a plastic bag for dirty ones!)
a change of clothing
a changing pad to lay the infant on when changing the diaper
a damp cloth in a waterproof bag for clean-ups
a sweater or blanket for cool weather
milk or formula