Maybe the nano or baby
I love both the Sac De Jour Baby and the Celine Nano Luggage bags. However, if i had to choose, i would buy the Celine Nano bag. The Nano is a small sized bag but can fit a lot inside. It is roomy, can be worn across the body, on the shoulder or hand held. It looks nice worn day or night. It can be zipped up as well which makes it secure. However, i do think the Nano is on the expensive side for such a small bag.
The Baby size Sac De Jour is on my wish list as well, but the only thing i'm worried about is the fact that it doesn't have a zip closure which makes me a bit paranoid to use it in busy crowded places or whilst traveling as anyone can easily put their hand in or things may fall out. But if you use a zippered pouch inside the bag then it should be fine.
I got the SDJ in the end. I have a Celine Mini luggage already and although I love Celine, it was nice to have something new