petit is good for running out with only the essentials. i LOVE mine, the deep red aged calfskin petit. and i'm a mom of three. it surprisingly holds enough. for example, i had a bottle of milk in a ziploc, of course, plus my pashmina, car keys, cell phone, sunglasses and some makeup, plus new bath and body works lotion and splash. and i had some space for more. sometimes i use it to carry my little one's diapers. it's awesome.
if you need a bigger size with more space, i would go with this order of your choices: cloudy bundle (so light and open you can throw anything into it), lux tote (love lux leather but i tried it ona few times at my boutique and find it a bit heavy and not easy to go over shoulder with big coat), GST (i find it heavy and too square).