For errand running, I have a nifty little thing that looks like a large wallet or a small purse. It unfolds into a changing pad, and has a pocket for a diaper, a few wipes, and a clean shirt. For the baby, not me.
For occasions when I'll be gone for half the day, away from running water, or out to a restaurant, I have a diaper bag. It contains:
Four diapers
Wipes
Clean shirt
Clean socks (the "heel strike into poop" is his best karate move)
Two small toys that only come out at restaurants
A plastic grocery bag
A flannel receiving blanket (it's a blanket! It's a burp cloth! It's a DESSERT TOPPING!)
Hand sanitizer
Hat
Pashima (acts as a second blanket, a nursing cover up if he gets too distracted to eat properly, or, when artistically draped about my person, covers my leaking personal bits and/or baby hork and/or pee s
pray)Now that it's cold, I keep a little sweater in there as well as the clean onesie, since he's a thousand times more likely to spill or spew on his sweater than his shirt. One of the side pockets has sanitary napkins, lip balm, and nursing pads.
And of course, I never carry a purse when I've got the diaper bag - I just transfer my cell, wallet, and a little travel hairbrush over to the outside pocket.