Both these companies (and perhaps others) have programs that allow you to turn in lightly-used clothing and gear in good condition for credit. You can apply the credit toward the full range of products, not just used. They do not accept baselayers or underwear, but it is good for jackets of all kinds, trousers, shoes and boots, and backpacks, etc. Patagonia only accepts their own brand, and REI only accepts products they have actually carried (but not necessarily purchased from them.
I sent some jackets I no longer wear (fleece, rain jacket, and ultra-light wind/mist jacket) and a cashmere sweater that I should not have purchased (too big at the outset) back to Patagonia and was surprised at how generous the credit is.
You can also shop online for bargains on jackets, etc. you need. They are not at thrift store prices, but still much less than you would pay for new items.