I am not a lawyer. This is not legal advice. Check with your school district's compliance officer or attorney if needed.

A booster club that applies the "benefit" to the ENTIRE student organization is generally not considered in violation. In other words, if your booster sells Thanksgiving turkeys and makes $15,000, and uses that money to apply to the cost of the trip as a whole for the entire organization, it's legal.

If the benefit ONLY applies to a few students, such as "this student's parents worked at the concession stand, so said student gets $40 off their trip cost" then that is considered an improper direct benefit.