Winning the lottery is something I’ve thought about many times! I’ve made plans already! 
One thing I’ve always been adamant about is that I absolutely would not go public. Not a chance.
As I rent, my first priority would be to buy a home. Have always wanted a barn conversion in the countryside so that’s what I’d have. I’d get a nice new car - no Ferrari’s or anything, just a nice 4x4.
I do wildlife photography in my spare time, so if I won a big enough amount to quit work, I’d quit and focus on my photography instead (and buy more equipment!) - maybe look at future business opportunities with it too.
I’d make sure my folks and my brother were sorted financially, so they were financially secure.
I wouldn’t broadcast it that I’d won. Just my parents and brother and they’d know how much I’d won. I’d give my two best friends some cash to help them, but probably fib about the amount I’d won. Not because I don’t trust them, because I absolutely do 100%, but just so I could give them an amount that I felt was appropriate and not sit wondering if they thought I was being too tight for not giving them more! (I don’t believe either of my best friends would feel that way at all, they’re not like that. They wouldn’t even expect any money - but you never know!).
The only person who concerns me is my DP’s mother. I’d absolutely give her some money, however she’d be the liability when it comes to keeping it quiet. I can trust my family and two best friends to keep schtum, but DP’s DM has a habit of opening her mouth about things you’ve specifically asked her not to mention to anyone else.
Maybe I should do a contract with a clause for her. That I’ll give her x amount of money, but if she tells anyone that I’ve won the lotto, then she has to pay it all back within 30 days