Dump everything out of your purse. Throw away old gum wrappers, napkins, binder papers, and clean your wallet of old receipts and empty gift-cards. Make a pile of things you need in your purse: keys, wallet, pens, beauty items, etc.
Organize your small beauty items by placing them in a pretty zippered bag. I like looking at the beauty collections on Sephora's website that come in cute little bags, but I wouldn't end up needing half the items in those collections. A cheap and efficient solution? Make your own beauty-bag! Be sure to pick a zippered pouch that is pretty because you will feel happy every time you open up your purse.
I tend to be low maintenance when it comes to make-up, so most days I only have my two-favorite lipsticks and a lip-gloss in my bag. My other beauty-bag essentials include: a small comb, tweezers, small scissors for bang-trimming "aha!" moments, Advil, gum, frizzy-hair conditioner sample, a small mirror, and an on-the-go concealer stick for those surprise acne emergencies. It might not be a bad idea to include a Swiss-army-knife. A sewing kit is also a smart addition when a button pops off your favorite shirt.
My purse only needs one extra bag to contain the clutter, but if you have a lot of items to carry you might need two or three different bags to organize your things. Perhaps you could use a bigger pouch to hold your cell-phone, keys, wallet, and snacks (so you don't ruin the lining of your bag with crumbs), and another pouch to hold your pens, pencils, and miscellaneous necessities.
To keep your bag well-organized and clean, look through it every night to throw away unneeded tissues and to reorganize your necessities if necessary. It only takes a few seconds and you will save time later by doing so.
Now that is beautiful!