To sell things well I think you need to do some research. With the CDs I'd start by using google to get suggestions for what to do with old CD collections. I would guess there isn't much you can do with them, but I'm sure there is a lot of advice out there that only people with big collections to sell care about. Go find that advice. For example, I found this as the second link when I looked for advice in getting rid of a large CD collection:
http://ask.metafilter.com/109058/Whats-the-best-way-to-sell-a-bulk-CD-collectionThe drum kit probably was listed for too much on Craigslist, or else you are in a very rural area. When selling on Craiglist you need to be realistic, if someone would spend $200 at an instrument shop for the used drums then ask $100. If they would cost $100 at a shop then ask $50. And whatever you ask, lower it every week until it sells, or just give it away if ti doesn't sell quickly. Just call a shop and ask about the value if you aren't sure, it doesn't even have to be in your town. But there isn't any one rule for every item you want to sell, it just depends. (At this point give the drums to the kid and be done with it, or see if he can afford $50 or some small amount like that)
So start by doing some quick research for whatever you are selling, shouldn't take more then five or ten minutes, and then apply that research immediately and ruthlessly to accomplish your goal. Don't get bogged down in maximizing profit, just get what you can, or give it away, and move on.
And I highly agree about the tax deductions if you itemize, they can add up very quickly, just use ItsDeductible to figure out the values.