I'd start with chance-based things which require no skill on my part in order to test the limits of this ability.

First, I'd flip a coin 100 times and attempt to get heads every time.

Next, to further test it, I'd roll a d6 100 times and try to have it land on 3 every single time.

Finally, I'd try to roll 100 natural 20s in a row on a d20.

Testing complete, I'd try to drive to work without hitting any red lights. I'd try to guess the passwords of all the locked phones in my forensic computer lab so we could lock up more child molesters.

I'd buy a lottery ticket with a reasonable and non-suspicious payout, maybe around 3 million. I'd try to pick stocks that would grow and grow that wealth until I could influence the market. I'd buy into companies whose products would further my personal goals: space exploration, fusion power generation, reusable materials science. Then I'd try to use my stock holdings to bargain for a position on the board of directors. Then I'd try to find employees who could invent cold fusion and room temperature superconductors.

At that point, I've pushed the boundaries of what I think would be achievable in my lifetime, so I'd try to think of something even better to do while trying to not die or age.