Edit because I don't read good I guess. I missed the whole "for a month" part. Assuming that means the stake is delegated, I can't have an effect on witness rankings, or redelegate to curation initiatives. Also, I'd have to let it go. Whoops :D

1. No self-vote. At 50m SP there's literally no reason. Curation rewards from $24000 in daily votes, even if voting at the very end, should be more than enough to live on.
2. Shake up the witness rankings. Some people would be happy and some would be sad, but one thing is for sure: things would change. And if I didn't like the results, they would change again, and so on.
3. Counteract bad actors. With 50m SP there would be almost no limit to my ability to negate the voting behaviour of bad actors on Steem. I needn't elaborate on who they are.
4. Drop random bombs. The idea of this has always excited me. Once a day I'd take a 100% vote and just drop it on someone. New, old, whatever. Someone who I thought deserved it.
5. Delegate to manual curation initiatives. I am not a wonderful curator myself, and I think that's okay, because there are some pretty great community curation projects here. I would use a large amount of my stake to support their activity.
6. Let it go. Slowly over time, I would power down and distribute stake directly by making purchases, giving donations, running contests, and similar actions. I would also burn a decent portion of it. 50m SP is just way too much for one person to have.