Honestly,
I would buy a decent sized house, big enough that I can make a built in movie theatre for say 20 people. Would also buy two dream cars (Honda Civic Type R, fully loaded and some type of beast SUV)
I'd then probably just go on vacation like every other month with my family do different locations until I have explored the world.
I would also invest a TON of it into stocks, just for the hell of it.

My immediate first move?
Take some close friends out to some super nice restaurant down in miami, pay for everything. Write them checks based on my relationship with them, nothing exceeding 1million.

Then I'd think out my plans for how to make more money off of it.

I'd hire an accountant

Buy gf

I like this idea, I've always dreamt that if I were to win it, and enough money, I'd give each of my co workers who I've spent the last 8+ years with and have become good friends with like $50,000 and just say peace out, it's been fun.

Easy. Pay off my house. Fix wifes car. Buy enough investments so I can make $8,000 profit per month. Keep $100,000 in bank for emergencies.
Start a campaign and donate the rest to abolish all religions.

Buy fg

Buy house and then make sure my friends/family are comfortable

300Mil hmm.

well 50mil to blow on myself/friends and w/e else. (house/toys/etc)
100mil in bank for straight interest.
50mil towards starting up charities or funding ones that focus on development not crisis relive.
50mil to reinvest

Tbh at 3mil in bank I'm happy, it equates to 34k a year after taxes and while that's not a lot its enough to never have to work or put up with people shit ever again.
I've fine with a simple life.

you forgot "Pay your debts"