At the end of the seder, it is traditional to say or sing " Next Year in Jerusalem". We sometimes think of this as a literal wish, though far fewer of us have actually found ourselves in Jerusalem for seder the following year -- congratulations if you have!

But Jerusalem is more than a place, it is a feeling, it is a hope.  At this point in the seder, 1/2 or 1/4 sheets of paper should be passed around to each participant, along with an envelope and writing utensil.  Folks are invited to write a brief note to their future selves inspired by "next year in Jerusalem." As metaphor: what is our own personal Jerusalem where we hope to see ourselves a year from now? 

Everyone seals and addresses their envelope to themselves, and the seder leader, or whoever is leading this exercise takes responsibility for keeping the notes all year and mailing them the following Pesach season.

This exercise can be done formally when everyone sits down to dessert or it can be introduced when the break for the meal happens and people can elect to write the notes at their leisure. 

I often have a basket out for people to drop their notes in.