I whipped up a quick doll diaper bag for Maia this weekend using a scaled down version of this tutorial (minus all the extra pockets because I was feeling lazy). It's a bit plain so I might add some sort of embellishment to the outside if I get inspired before her birthday.
And here's what's made it into the bag so far: four little doll diapers, a couple of scaled down burp cloths, a small stack of cloth wipes, a flannel receiving blanket, a rattle, pajamas and hat for the doll, and a pair of impossibly small baby socks. Thank you everyone for all your suggestions! I'll probably add to this (small board book, another outfit, etc) as I come across possibilities or feel like sewing more.
And, just so you know, I'm undertaking a baby doll rehab -- results to be determined... I briefly considered the doll hospital option but being the frugal do-it-yourselfer that I am, I'm going to give it a go first.