Consider the items below when making purchases of officer supplies. 
Discounts:  Some office supply vendors grant discounts to their business customers.  These discounts are granted on a percentage (5%, 10%, 20%) discount for purchases made over a certain value.  Find Discount Coupons from office supply retailers.  Retailers are always offering discounts throughout the year and especially on holidays.  Be on the look out for them.
Rewards:  earn points that you can use to get discounts.  Points are based on purchases made, items recycled, etc.  Depending on the vendor Points may or may not be carried over from month to month or quarter to quarter.  These Points can then be used to get discounts when you make purchases.
Membership:  Many office supply vendors offers the opportunity to signup for a membership account.  This benefit allow you to get more personalized treatment whereby an account manager is assigned to you to assist you with making future purchases.  It also gives you access to better discounts and even credit to make future purchases.  A membership account lets you track your purchases and points earned.  Membership is usually free.  There are different levels of membership depending on how much is spent.  You have to spend a certain amount within a month or quarter to qualify for different levels of membership.
Free Delivery:  Many office supply vendors also grant free delivery to customers that make large purchases.  A minimum amount is usually estabished before the free delivery is granted.
Online Purchases:  Online purchases can save you from having to pay sales tax from Internet purchases.  To be certain of getting the tax benefit you have to purchase online from a retailer that does not have a physical presence in your state.  More and more states are passing laws that require retailers with a physical presence in their states to collect taxes from online sales.
Bulk Purchases:  Making bulk purchases will get you above the minimum purchase threshold in order to get discounts.  Don't run out and buy an item everytime as soon as you runout.  It is best to waint until you're ready to make a purchase for many items.