Acorns (From the money tree)
Another instance in which you can almost literally go outside and pick up money off the ground! You are only limited by your ingenuity because there's a market for everything. Large acorns with their caps still on are highly desirable as decorations. All acorns can be sold however and ugly decrepit acorns without their caps are often sold on eBay by the pound for animal feed. So if your kids are bored...
Bottle Caps and Lids
Selling bottle caps (particularly vintage ones) has long been known to be a highly profitable enterprise on eBay. Since my husband and I don't drink either alcohol or soda, we don't have much opportunities to gather metal caps. Instead, we decided to follow the advice of Kara over at SheThrifts and save our caps from all sorts of bottles! (Check out here story and how much she made here). While we can't claim to have become rich overnight, we're making money on what we used to consider trash and throw out!