I quickly created the sheet above for the students to use for the activity. For their Shrinky Dinks, I asked them to create a drawing of themselves on a quarter piece of an 8.5x11 Shrinky Dink paper. I told them that how they chose to draw themselves is up to them - I didn't have specifics of what I was requiring their self portraits other than to keep it from the waist to the head (just for shrinking purposes). Once they had their drawing completed, we shrank them in a toaster over and they had to then write a message to the future 4th graders. This could be advice that they have, things to look forward to, or how they overcame difficulties.
I put the student recorded messages below (click here if you are unable to view). I am going to share the video with the current 3rd grade teachers so that they can show their students. The future 4th graders have a lot of great things to look forward to next year!