If I won the powerball at $100 million, I'd take the ~50% cut for immediate payout, so it'd be $50 mil, so, after another third out for taxes, I'd have about $33 million. $1 million to pay off all family debts and mortgages (the largest single debt being my ungodly law school loan debt). $5 million on a brownstone townhouse in Brooklyn ($2 to $3 million for the property, the rest in a fund for upkeep and taxes). I'd put $5 million in a trust for my sister and mother, limiting withdrawals to about $120k a year for 20 years. I'd put about $1 million in easy-to-access accounts for living expenses, and invest most of the rest of the $20 million in a mix of conservative long-term investments, like index funds. I might put about a million of that twenty in easier-to-convert short- and medium-term investments, too. I'd donate the last million to my school district growing up so they could buy and maintain a bunch of school-owned musical instruments for band and orchestra students to use.
First, I'd take my girlfriend out for a lavish night on New York City. Then, I'd quit my job and do pro bono legal work part time for a couple of foundations here in the city. I'd also travel around the world and meet up with buddies from college in Europe and China.