Another good one: Bagmate!
www.bagmate.com
It's like a bag within a bag...but really, they're so cute if you wanted to use them as a bag you definitely could, and I have.
Black microfiber exterior with leather handles that retract, interiors are lime green, hot pink, lavender or tan.
When I first started using them, I thought "What a pain...I have to organize everything inside the purse inside the purse!" But then I had an emergency where I had to use another bag with just essentials and by the end of the day, I was begging for the bagmate.
I use it in every bag I have except the Bal. Courrier, which is huge. That's the only problem, I guess. Most of the organizers work great in bags that are only slightly larger than they are, or if they close at the top. If you have a huge bag, like a hobo bag or one that is not too structured, the bagmate will roll around inside and your stuff will fall out. So there's no point.
It works beautifully in my LV Noe, baby Spy, LeSportsac Fafi tote and Marc jacobs hobo.