Does people like Warren Buffet and Bill Gates keep their fortune in the bank?

Rich people seldom have money sitting in a bank. They own property, shares, homes, investments, etc...that's worth billions. If they do have "cash" or any other liquid assets, those are usually locked up in a Swiss bank account, or some other off-shore bank (in the Cayman Islands, or something like that) where they don't have to pay taxes.

I'm guessing most of the money is in the stock market, but I'm sure they also have money invested in hedge funds, real estate, and bonds . . . and I'll bet Mrs. Gates has a few choice pieces of jewelry and art. (Mrs. Buffett is dead, and Warren doesn't seem like the artsy type.) They keep relatively little money in regular bank accounts.

For most folks, most likely particularly Buffett who made his money in investments, their net worth is comprised of many many holdings. They certainly have a bank account or two, but in addition to investments in things like securities also own companies, which include physical capital like buildings and equipment, not to mention land and all the associated rights, brands, and more things than we paupers can begin to imagine.

they diversify...have many different kinds of investments in their portfolios. Like real estate, loans, trusts, tax shelters, restaurants, gaming places, stocks, they give money to organizations and for scholarships, etc.

Yes, maybe for their retirement ??

but mostly (95% or more) will be in stock market, cos they aren't stupid at all.

no- they keep em in the stock market!!!

hahaha, they didn't get rich by being stupid