One example is timing the time it takes to complete a crossword puzzle. But for that to be a meaningful metric, you would have to already be pretty proficient at crossword puzzles.
You can test reaction time by having someone drop a ruler between your hands and seeing how long it takes for you to react and stop the ruler's progress by clasping both hands.
Maybe there's a program out there that will generate a page of arithmetic problems. You can print it out and see how long it takes you to complete them.
Or you could get a d100 (or two d10's) to generate numbers that you would have to multiply either in your head or by using an abacus.
If you come across anything else, be sure to share!