Your best bet for affordable loose-leaf paper and pens is to stick with the big box stores like Target and Wal-Mart.  They generally have the best prices for back to school supplies.  But it's totally worth your while to watch the ads in the Sunday paper, sometimes grocery stores will offer fantastic deals on one or two essential supplies. Staples, Office Depot or Office Max will also do blowouts on one or two essential items too. It pays to watch the ads and look for coupons on basics like pens and pencils.

Don't forget to re-use items from previous years ... you may find you're able to use folders, notebooks, and binders semester after semester.

Stock up on items your going to use a lot of during the year while they are on sale. You may not find the same deals at the beginning of Winter Semester as you did for Fall Semester.

Clothes

Here are some tips that worked in my family: 

My parents budgeted what they could for new school clothes (which at the time was $100).  This money was to buy all the clothes I would need for the whole year.  My parents explained this to me, and told me what my budget was.  This taught me to evaluate what I thought I would need for the whole year.  My list usually consisted of a new pair of jeans, a top, a sweater, shorts and new shoes (I actually recorded in my journal one year what I bought and for how much!!).  I would then study the weekly ads in our local newspaper so that I could buy what I wanted at the cheapest price (see, the Deal Diva tendencies started when I was young!), this way I was able to stretch my $100. 

This is a really good idea if you have older children, this teaches them to be responsible with money and to understand the cost of clothing.  When I got a part time job my parents gave me less money and told me that it was my responsibility to pitch in some of my own money.  If you have younger children, the concept can still work, only you as the parent get to do the hard work.  Set a budget of what you can spend on each child, and then make a list of what you think they will need all year (winter and summer clothes).  Remember to check the weekly deals on the deals link to see what is on sale each week, and then just watch for the best prices on the items your children need.

 Books

This mostly applies to college students.  After five years of college these are the secrets that I learned.

• General English books are easy to find at used bookstores (no, not used at the school bookstore) and sometimes they are even cheaper new at Borders or Barnes & Nobles than they would be new or used at the school bookstore
• Are their people in you ward or your dorm that have your same major?  Check with them on what classes they are taking and if they would be willing to save their books for you, or sell them to you at a discounted price.  Be sure to offer to trade any books that you have that they may need.
• Some Colleges offer “buy back” programs, SELL SELL SELL!!!  At the end of the semester take your books back as soon as the final is over to get the maximum back for your book.  Save this money for next semester’s books.
• If you have the time: Comparison Shop, my college town had 3 college book stores, I would make a list of all the books I needed and find out where I could get them the cheapest.
• Wait to buy until after the first day of classes.  I cannot tell you how many “recommended” but not required books I bought that I never once read!  Those books are also usually the ones that the bookstore won’t buy back at the end of the semester.
• Share: do you have a roommate who has the same class, same book, but different professors (this is important so no one fights over the book before a test).  Offer to split the cost of the book so you can share it for the semester.