If you’ve ever wanted to send an email to your future self, there’s a great website for that!
You’re welcome to use this website for free, and it does exactly what it says on the tin: You write an email to your future self, and FutureMe promises to send it to you at the date of your choice.
I can imagine a lot of positive uses for this, but if you need examples, check out their FAQ page and their Public Letters page for more info.