Craigslist.com is a huge help for life in general. Need a canopy for a tail gaiting party? Need a few boxes of Christmas ornaments? Need a short term job, or do you need short term help? I have bought and sold so many things on craigslist, and met many nice people. I've sold stuff that has been cluttering up my basement, garage, life, and gotten paid cash in a matter of days.
There are also things for sale on craigslist, that you can turn around and sell on eBay or Amazon or somewhere. Once you establish an area of interest, things you know something about, do some research on how they sell. Then if you see them available at a good price, online or at a yard sale, you know enough to buy them.
Tools sell very well, books of course, and toys, in good shape. There are many, MANY other niches for you to develop. Look around you, jot down some things you see. Notice how many you see in other places, besides your home and office. People love stuff, so sell it to them!
The longest journey begins with the first step.