Nowadays, the internet makes selling your old stuff easy. It never hurts to make a few extra bucks on something you were going to throw out anyway. Here are a few examples:
Instead of tossing that textbook you don’t need anymore, try to sell it back to the student store. Most colleges these days will buy back that book that you used as long as they are still using it next semester. Depending on the need, it may be possible to get back over 50% of its new dollar value. Since textbooks are upwards of $200 these days, that can be a significant chunk of change.
Instead of throwing out your old phone, try putting it on ebay or craigslist. I had an old iphone which was about 3 years old, and just finished my contract on it. Since I was getting a new one, I ended up putting it up on a classifieds website. It turns out that old unlocked iphones were quite high in demand, and I was able to get around $260 for it. Not bad considering otherwise it would have just been collecting dust in a a box somewhere in my room.
You can do the same thing with old furniture and appliances. If you don’t know how much to ask for it, you can do a search on similar items, or you can just say you’ll take “best offer.” There’s really no reason not to at least try, a few extra bucks here and there adds up fast if you have a lot of stuff.