Rescue battered wood. Pallets and pallet stock are cheap (or free) and easy to come by. Look for untreated specimens at construction sites, community colleges, buildings under renovation, or shipping warehouses and plane them down and/or kiln-dry them in a homemade kiln-dryer to uncover their hidden beauty. You can then resell the wood as is or even turn it into beautiful furniture. (Be sure to advertise that the wood is “reclaimed,” as people are often willing to pay much more for this.)
Start a website or blog. Sure, competition in the online world is steep, but one thing that makes a good site or blog stand apart is the dedication and enthusiasm of its writer. Plenty of sites focus too hard on SEO and keywords, and while SEO-optimization is certainly necessary to help your content make money, delving into something that truly matters to you will set you apart from your fluff-and-stuff competitors.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.