About the time I finished college I read a newspaper article about packing for travel ... but what caught my eye was a comment that anything you buy, you should assume will last you a decade. At first I thought, "No way. Nothing I buy lasts that long!" But as I considered it, I realized it was because I was buying cheap-o stuff that didn't wash well, showed its age quickly, and needed replacing fairly soon. I started trying to buy nicer quality items, and I found that they did wash better and did last longer -- meaning that they were cheaper in the long run. I also avoid buying trendy things. I don't wash lightly-worn items every time they're used, and I wash almost exclusively in cold water and hang many of my tops and delicates to dry.
What lasts me ten years: Dresses; most of my work dresses come from Lands End (they go on sale for about $20 at the end of the season). Sweaters, dress pants, dressy shoes.
What doesn't last me ten years: Jeans and work shoes. Of course, I have a small selection of these things -- fewer than most people have -- so mine are worn more frequently.