How about alongside an interstate highway?
Not just on interstates. I often pick them up while riding my bike on rural roads and state routes, and some of them look like they’ve never been used. I’ve also found a lot of microfiber towels, gardening gloves and pots, hex wrenches and other tools, coins, and a couple bunches of keys and cell phones.
Supermarket delis.
Ace Hardware and Harbor Freight tools will sometimes have promotions where you can get a 5-gallon bucket when you purchase a certain amount. The buckets are new and clean.
While they are not free, 5-gallon buckets can be obtained from Firehouse Subs. Firehouse Subs uses the money as a donation to Firehouse Subs Public Safety Foundation.
We have a couple of yogurt bowl businesses nearby. They receive their yogurt in large buckets and regularly give them away.
It has been a few years but we gave them away when I was a fast food manager.