You didn't have to live in the 70s to enjoy the decade. Wear bell bottoms, platform shoes and loud colors. You can purchase a 70's costume, or simply raid your parents' closet. You could also possibly find 70's clothing from a thrift store. At the rally, play popular 70s songs such as "YMCA," "Stayin' Alive" and "Play that Funky Music." Get the crowd involved by having the football team come out during "YMCA". Sing along with the song and tell the crowd to chant the school's acronym. For example, if your school is Cape Henlopen High School, say "CHHS."
This is one theme that the ROTC team at your school will definitely appreciate. Have your classmates dress in fatigues or camouflage shirt and camouflage face paint. During the rally, have the football team come out in military formation. Have them chant a song that involves the opposing football team. For example, if your opposing team are the Vikings, the football team can chant, " You might be good at baseball, you might be OK at track, but when it comes to football, the Vikings better step back!"
Celebrate the wild west with a cowboy theme. Have your school dress as cowboys. No one has to go out and get an expensive cowboy outfit. Flare jeans, cowboy boots and a western shirt is sufficient. Again, students can raid their parents' closet or check out a thrift store. Play saloon music during the rally. Have your football team come out dressed as law officers with the quarterback as the sheriff. Have a few members of the team dress as cowboys but instead of western shirts have them wear T-shirts with the opposing team's name on it. Have the players dressed as the opposing team come out in handcuffs.