When I head to the flea market, or am out shopping for fun new additions to the apartment, I carry my Trusty Little Designer's Helper Pouch. Okay, it's not really called that, but the name does kinda fit. When you have your handy, dandy pouch along with it helps take the guessing out of whether a flea market or yard sale purchase (which, do remember, you can't return) will work when you get it home. Or whether that fabric or accessory will compliment your living-room paint. If that pillow will really offset the sofa color the way you've been envisioning.
I personalized this interior designers’ kit to suit my own purposes. I found a cute zippered fabric case (clear plastic case, or even a cosmetic bag works just as well, if you like to be able to see your tools and find them quickly and easily). I'm just a sucker for fabric and pattern. Here are some really cute fabric pouches you'll be proud to carry, from this great etsy shop Three Green Apples.
Inside, I carry with me a small tape measure, notebook & pen, my room and furniture measurements or floor plan, fabric samples, swatches and paint colors for the various rooms I'm working on at the moment. For inspiration, I throw in scraps of ideas and my wish list for design projects or objects I might be hunting for. With all of these tools accompanying me, I'm feeling a bit more comfortable about those spur-of-the-moment purchases. It's kinda OCD, which I admit I am, but it does come in quite handy, indeed. Oh, and it's always good to carry your digital camera along too, if you need to take a quick snap should you need to give a purchase a bit more consideration.