I heard this game from a friend of mine years ago. I called it a smiley jar. 🙂 It helped me a lot when I went through a tough and uncertain period. I was newly arrived in London and was working in a small coffee shop. I was full of hope but also doubts about my life in a new and unknown country.
My added suggestion is you do not have to wait until the New Year’s Eve to empty your jar. You can read through all of the post-its whenever you need to boost your energy and mood.