Back To School Clothes Shopping

With two teenage girls, back to school clothes shopping can be a nightmare!  My girls are both girly girls, and into the newest fashions.  Unfortunately, my budget is not as fashion forward as their tastes.  To try and ease my pain, and teach them some frugal skills,  I have come up with a game plan that we have used the last few years.  It teaches them money management, and I have no credit card bills looming!   Through out the school year I am saving up money and putting it in an envelope for each child.  They each get a set amount and that is what they are allowed to spend on new school clothes for the year.  I also gather as many store coupons as I can and offer those to the girls to use.  I do buy 3 pairs of school shoes and each get several new pairs of jeans at mom's expense- BUT, they are at my price points!  If they feel the need to get a $50 pair of jeans, I will pay up to my set amount and they are responsible for the difference out of their money.  So far this system has worked very well.  After the first year, my oldest learned not to buy everything she saw at the first store we go to! 
My youngest always seems to do the best at this system, but she is much more like me in the frugal department.  They have learned to look for mix and match pieces, check the clearance racks first, ask mom if their are any coupons for this store and watch for sales, esp BOGO.  We also have several stores/shopping malls in our area.  They have learned Mom will go to each area once, so we consolidate our trips to make the most out of them. 
I also have a younger son who is not into shopping as much as his sisters.  When you need to take a 4 year old boy with you, you also need to make sure you are prepared!  We eat lunch before we go so as not to need stop for food.  I pack some snacks in my bag for my little guy, and some water bottles in the car.  I also take paper and crayons to help keep him busy while we are waiting for the girls in the fitting rooms. 
It is 2 weeks before school starts here and already my girls have their first few outfits picked out and ready to go! My oldest only has a few dollars left, and my youngest still has 1/3 of her money left!  Looks like a few more shopping trips to go.....
How do you prepare for the costs of heading back to school?