Some things I have done:
- During a career slump I joined the Project Management Institute and was about to get a certification before I got so busy I had no time for it. The PMI certifications are a good balance between affordable and meaningful.
- I did all the Python problems on HackerRank; this was a journey, like climbing a mountain, I learned a lot, had fun all the way, got practice for interview problems, etc. (I've seen other courses in other languages at that site and some others, but that one is in a class by itself -- I printed only my HackerRank Python certificate to hang on the wall because I am proud of it.)
- I challenged myself to print something every day to keep my inkjet printer from clogging up, but now I go to auctions and buy the cash registers from failing stores just to get the receipt printers, which I break the way a rock star breaks guitars. My son feels like he has to outdo me, so now he is making big anime art prints by putting together 8x8 inch squares.
- My image technology obsession has gotten me into arduino so I can build devices that paint images from a 1-d strip from a moving platform like an automobile. That's gotten me to rethink programming from the ground up.
If the imaging side projects go the way they are going there could be a day that somebody sees something I did that was different from anything they'd ever seen before and then work finds me. That was how I got "too busy" to get the PMI cert.