Pay for my parents to have the dementia care they desperately need without being forced to sell their home.
Say to DH he can quit the teaching job that is running him ragged and never have to work in a school again.
Donate to the NHS neonatal unit that saved my daughter's life. The NHS also gave her the gift of hearing through cochlear implants so I'd make a sizeable donation to fund further research to make implants even more effective. (At present my daughter's implants allow her to interpret speech but she has no appreciation of music as the implants aren't advanced enough to interpret different pitches - as a musician, it pains me that I can't share my love of music with her).
After that, I'd buy a home for life, for my family to grow into, rather than living on top of each other in our current shoebox.
I'd pay off the mortgages of all my friends who have been there for me when the shit has hit the fan, easing the pressure for them.
I'd travel to all the places I've wanted to go but previously couldn't afford - South Korea, Japan, Australia, New Zealand, and British Colombia to name a few.
And with the money I had leftover, I'd get laser eye surgery, get my crumbling teeth fixed, have regular deep tissue massages to ease the trapped nerves in my back, and buy the most mellifluous, custom-made violin imaginable.