If there’s one thing my old grandpa taught me when I was a kid is was to make sure that if I were going to stir a solution containing fissile material in a cylindrical container to make sure there wasn’t enough material in the solution to become critical.
I remember his advise every day.
The top answer for me is always a good cast iron pan. Doesn’t have to be expensive but should be quite heavy. It’s not just buy it for life either, it’s buy it for future generation’s lives.