Here is an idea:
Squat/Bench Press - superset one thing with each movement
Deadlift/Press - same superset idea (box jumps/chins, for example)
Friday - assistance
Set up stations: push-ups, fat man rows, dips, leg raises, jumps, swings, etc. Set a number of reps per station, have them go through each 5-7 times. You may have to be creative depending on what you have but you cannot go wrong with basic bodyweight stuff.
Think about it like this: If you could create a team of badass senior kids, not just athletes, kids. Confident, strong kids. What would you demand from them physically? Barbell training is a start but give yourself time to step back and look at things "bigger". What physical skills should they be able to do, regardless of life goals?
I'm amazed these days how weak kids are as they are not given formal PE in their younger years. I remember being embarassed that I could only do 11 chins when I was in 6th grade. Our school had something like 75% of the boys (not athletes) run under 7:30 mile in junior high. So think about it in terms of big picture. I'm hoping the age of specialization has run it's course but we still need to give kids some kind of base to work with for a better life. There is NO detriment to being a strong, in-shape person.
Being a HS coach with limited time is not easy - especially when we pay such lip service to health but are given no time, few resources and zero support. Hell, more money is spent on AWARENESS than PREVENTION. I applaud your efforts and to me, you are a hero.