i do this! lol, actually i never did this, untill i got my cabas raye gm. its a beautiful bag but really big and its so hard to keep everything in order, so what i did was try to put all my essentials - wallet, cell phone, keys etc. in my regular mono pochette so i can a) keep everything i use alot organized and also so b) if i have to run out somewhere, but don't feel like carrying a big bag, i can just grab the pochette and be on my way.
lol! that's exactly what the SA told me when I was buying my 35. Now I'm gonna buy a mono pochette too as a makeup case/purse.