You need to also download my graduation letter (for free) in conjunction with this.
Have students do this in ELA or Social studies the first week of freshman year. Make sure they know only they will see it - you will never open it. If they pass away, you will give it to their families. Tell them it's important to take it seriously because in 4 years when everyone is opening their letters, if theirs is silly, they will feel bad. I've done this for 10 years and kids who don't do it or don't take it seriously ALWAYS are disappointed. Tell them they can always come and add to it but can't come take anything out. I recommend they put things in it such as money, pictures and/or or notes from important people in their lives like mom, dad, best friends etc... Tell them they will see what kind of renaissance they have over 4 years. Tell them these are only guiding questions - they can write about anything.
I do this as part of our renaissance era - being secular and focusing on themselves instead of religion.
I color code my notes so the red would be the stuff the kids write. Feel free to change whatever you want.