The best sample for estimating the number of students who bring their lunch to school every day would be 80 students selected at random during lunch. This sample is most representative because it includes a wide variety of students and reflects their actual lunch behavior in a specific context (during lunch time), allowing for a more accurate estimate of the overall student population's lunch habits.
The other options are less ideal because they are limited to specific subgroups (e.g., only female students or first-year students) or a specific club, which may not represent the entire student body.