This is a great prayer activity that you will need to announce in advance. Inform your students that they will need to bring an old t-shirt to student service next week. During prayer time, have students go around the room and write a prayer request on their shirt. Then divide students into groups to pray for the requests. Student can take the shirts home for continued prayer.
We did this activity several years ago and I still see students wearing their shirts with the prayer request all over them. I still have my shirt hanging in my closet. This is an activity that people will not forget.