Take advantage of sales when they are happening! Make a list way ahead of time for the supplies you will need. Pencils, rulers, staplers, socks, shorts, doesn't matter. If you need it...put it on the list. If you have a kid in college, make sure you put the dorm supplies on the list. Non-perishables for the college student can be bought ahead since they won't go to waste, and they can go to school all stocked up.
Every time you go shopping whether in stores or on the internet, look for bargains that may be on your list. If you start buying ahead, you can avoid the old trap of getting one item on sale and paying more for the rest, since the stores are clever that way.
By the time school starts, you will be armed and all the richer from your savings.