Actually it has been a considerable strain on my brain to keep making up new stuff for an entire month. It's been fun and rewarding but very challenging.
Early in the month I was just copying and then expanding on pictures of some old toys. A couple of those toys were similar to something I'd had as a kid possibly second hand things. I dimly remember a couple tin toy wind up robots from early on, but they may have belonged to someone else. They were brightly painted, but rusty.
I've also lifted from some very old sketches of my own design.
Drawing is fun and exhilarating, but eventually it can be exhausting as well even if you're working from a model or a previous idea. The more creative it is the more it makes your brain sweat. Illustrators and comic book artists who create whole cloth from the imagination all day long have my admiration. I've never actually had that experience.