I have to carry a purse for everyone else's crap. Two changes of clothes for DS, because he's not always a straight shooter, or sometimes we just don't make it in time. Also gotta have room for babies and trucks that they get tired of toting. DH doesn't usually need me to carry something, unless we're sneaking candy into the movies, or we're at the zoo/park and then I have snacks and drinks for everyone.
For myself I carry very little. When I had a wallet phone case, that's all I carried. Today I carried a clutch with my wallet, phone, keys, and Chapstick. That's it!
If they made women's jeans with nice deep pockets, we'd never need a purse. Then again, I like to carry my coloring book, planners, journal, etc. So I like a nice big bag, so long as it's cheap.