Here’s an idea I discovered on BBC’s “Tightwads” documentary about extremely frugal people. This particular gentleman put a five gallon bucket at the end of his garden with a sign labelling it “Ye Olde Wishing Well.” On Friday, Saturday and Sunday, passers-by would throw money into the bucket, which he would collect on Monday.
If you want to watch the entire documentary, here is a link to a playlist of it on Youtube.