Keep a list in the front of your calendar or day planner. See how many items you can add to it that you will never have to buy again.
Some include: waxed paper (cereal box liners); memo tablets (use all scrap paper); pens (use free ones); scotch tape (use misc. labels from stamp edges and junk mail); dish rags (use--rags!); plastic containers (use ones margarine & other foods come in); wash cloths (cut up & hem worn towels); envelopes (make your own from scrap paper and junk mail); lip gloss (make your own by mixing a little petroleum jelly, ends from old lipstick & a couple drops peppermint extract); window cleaner (use ammonia & water); household cleaners (for most purposes a little dish liquid in water does the job); paper napkins (use cloth); paper towels (use newspapers or rags); plastic wrap (use saved bread and other food product bags); you can see your list can get quite long.
Try to add a few more items to your No Buy List each year.