First thing's first, let's empty out that bag! Dump it completely out. Shake out the crumbs; wipe down the outsides or any sticky or smudged parts.
Take a look at what was in there. Items that make sense in this kind of bag: wallet, phone, keys, anything else you'd need daily - like a calendar or notebook. Set those aside.
Then, let's look at all those little papers and receipts. Do you need them for any reason still? Toss it, if not. If you do put it in one of two places: the proper file or in a place where you'd need to access it. For example, if you need the receipt for a return, stick it (literally) to the item and get it in the car. Or, if you're not sure if you'll return it yet, keep a small ouch or envelope for those slips of paper. Keeping it in your bag or the car door might be a good place to store the pouch. Just remember to weed through it from time to time!
Lastly, take a gander at what's left. Make-up, toys, tissues, all those things. Whatever simply needs to be put away elsewhere should do just that. From whatever's left decide if it should live in this bag. Maybe carrying snacks and lip gloss makes sense for your daily or weekly routine. Maybe a map doesn't need to be in there now that you're home from vacation.
Finally, don't just toss it all in there! Most bags have compartments and zippered pockets. Use these! Keep like items with like - just like organizing any other area. If you really have a cavernous bag, consider getting an insert for separating things. There are purse organizers available, as well as good ol' fashioned zippered vanity bags. Now you'll have a reason for keeping all those free make-up bags from the department store counters!