Very infrequently. For everyday I use a very old backpack, ugly and not sophisticated at all, but just too darned convenient. Everything fits in there and leaves my hands free--the beauty of backpacks!
If we're going out I'll switch to a pretty little bag, for days I'm going out and doing harp stuff at harp friends' homes (seems often lately), a bigger over the shoulder bag that fits my music and other stuff in it.
Do you wear flat comfy shoes to work or heels?