Look, I know it’s not always realistic to pull these off; I personally wouldn’t bother trying. But if you’ve got a ton of stuff lying around — not outright junk, but stuff you don’t need, like the aforementioned DVDs and kid’s clothes — it’s worth a try. Advertise on Craigslist and put up signs in your neighborhood, then come Saturday haul a table out to your driveway (assuming you have a driveway), load it up with stuff for sale, and take whatever you can get.
The folly of youth is believing that there's always enough time for everything. Youngsters often believe that retirement, or wealth building, is something that comes later in life, and are more preoccupied with the concerns of the now. Unfortunately, this often leads to a cycle of "Oh, I should do that next month," month after month, until before you know it, you're 10 years older and you've missed out on a decade's worth of compounding interest. The first step is to stop procrastinating; saving and investing is scary, but the longer you wait to do it, the fewer advantages you have.