I love the idea of a messenger bag. They are the BEST, IMO.

I have a really great pattern for one if you want me to trace it for you. It is easy to make and doesn't have alot of pieces.
This is what I would stuff it with:
Matching zippered bag for "essentials" while on the run
Water bottle with one of those freezer sticks to put in it to keep it cold (I have seen them at WM for around $2.00)
Trail mix or granola bars (for when she is on the run delivering babies)
Sarah/snugbug's oragami tissue cover w/ a couple packs of travel size tissues
Fabric covered journal
Nice lavender or tto hand lotion
Burt's Bees lip balm
HTH and make sure you post a SnS with your finished product.