-have a snack stash for kids that don't get to eat dinner between football/cheer/cross country practice and band practice. For some kids the only consistent meals they get are at school.
-have a "carrot" song that you're going to work during after school rehearsal. I know budgets are a real thing but if you find a song that the kids really want to play in the stands, it may get them to practice. Our rehearsals go from 5:30-7:30 so I use the first 30 min to work on stand tunes that the kids want to play. Then as the football players trickle in from football practice we transition to our show music and drill.
-talk to your upperclassmen and leadership students. some of them may need to go pick up kids who don't have a ride to practice.
-plan some sort of social component to your rehearsal. Whether it is a game or a section competition, students will try harder to make it to practice when they feel like being absence will let their section down.
-give frequent back breaks to the percussion and tubas. Sometimes kids don't want to complain but they're having trouble holding their instrument for extended periods of time so they skip out on practice.