"Put it in diamonds or something like that."
Diamonds are a bad bet in the long term. Platinum, on the other hand, is a very good bet. Not only is it valuable for jewelry purposes, but for many industrial purposes, as well. It's also in much shorter supply than gold, the other hedge metal of note.
Diamonds are used for a great many high-tech purposes like lasers, although in 200 years those uses may be obsolete.
The big advantage of diamonds is that you can easily carry several millions of dollars worth in your pockets.