The Park West Bag - I think this one might be it! Finished size says 18"x13" (doesn't say how wide it is at the base), which should be plenty big enough for a file box and supplies. There are pockets on the outside for phone/keys. I'd like to add a couple of pen slots and maybe a small pocket for my post-its so those aren't rolling around all the time.
I made this for a friend! Outside layers are baby blankets with gerber daisies. Inside there is everything!: Diapers Jumpers Johnson&johnson lotions n bubble bath Soothes Bottles Wipes Spoons etc.. Basically a mini baby starters kit! So much fun to make as well! Even more fun to watch the mom or mom to be unfold a never ending amount of items!