Plaster the walls of the locker room with encouraging posters for the seniors on the team. Signs can say things like, "Way to Go Seniors!" and "Good Luck Seniors!" Decorate the posters in the team colors. Another idea is to place individual pictures of the seniors on the team on one of the posters and with the words "Thank You Seniors!" on it.
Decorate the locker room with balloons in the school colors. Use the balloons to create a balloon border for the senior posters, or tie balloons to each of the senior's lockers. Cover the ceiling with the balloons in the school colors. Another idea is to decorate with mylar balloons in the shape of footballs and football helmets.
Create a personalized locker decoration for each senior. One idea is to create a football jersey out of kraft paper and decorate each one with the last name and number of the person, just like on real jerseys. Write "Senior" underneath the number. Do the same thing with Football helmets. Another idea is to write the senior players team stats on back of the jersey. Include a picture of the player in action.
Surprise each senior with a candy treat bag attached to his locker. Give each senior a bag filled with candy-coated chocolate pieces in the school colors. Place baked goods such as cupcakes with frosting in the team colors in their lockers. Write out "Thank You!" on the cupcakes in gel icing. Include an energy-boosting trail mix with a note attached that reads: "We're nuts about our Seniors." Come up with these types of saying for any special treat you choose to give the seniors.