For large course field trips it is common for instructors and students to show up at different times, which means that instructors will usually carpool with other instructors, and students with other students. To set up those carpools it would be helpful if the "Email Participants" screen had a way to quickly select participants based on their role, i.e. all instructors, all students, all leaders. Yes, it's currently possible to use the per-person check boxes to this now, but some large field trips (Navigation, Snowshoe, Scramble) can have as many as 90 participants, so selecting them individually is tedious and might be enough of an obstacle to discourage people from trying to carpool at all.

Ideally this would be implemented in a way that populates the checkboxes of the relevant group of participants but still allows the user to alter the individual checkboxes before sending the email. This would allow people to quickly narrow down the roster to the relevant group of people (e.g. "all instructors") but continue to refine the list based on criteria such as geographic location (e.g. "all instructors who live near me").