Blocks of any kind
This one is simple, yet encouraging. He was an avid builder, but generally likes to stay with the same building materials. So, for this one, I chose a set of blocks that he doesn’t typically use. I thought maybe putting them in a different environment such as outside, would encourage him to use them.
Now while my idea was when I thought would work, it didn’t. He was usually using magnet tiles or wooden blocks, and these ones are bristle blocks. I do notice that they are a bit more difficult to build with, but they’re much more durable as far as being able to get wet and dirty. This activity could also be extended washing once you’re finished!
It may not have worked for mine as expected, but maybe it’ll work for you. All children are different, resulting in activities that end in their own way.