Fritz has some great input below. In addition, you might consider:
- Did the leader clearly explain the learning objectives for the event?
- Did the leader identify how modules are to be executed, what specifics to watch for and how to score or evaluate the students?
- Was the debrief effective in enabling discussion about salient observations or guidance from the event?
- Did the venue after the event have tasty food? (maybe ignore this one!)
- Do you think the mood or atmosphere fostered a positive learning environment?
- Did you have fun?
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First I would remove the student-specific questions, i.e. rating the instructors, the feedback received from instructors, did you learn a lot, etc.
I would structure the questions around the efficacy of the field trip environment with respect to the teaching goals, i.e., ask whether the instructors thought the student-to-instructor ratio was conducive to effective teaching, whether the duration was appropriate (too short / too long?), was the general preparation for the FT ok, whether the chosen location was good, etc. We could ask if the instructors have feedback on the students - i.e. were the students prepared or not, and if not what can we do to make sure students come with the right expectations and knowledge to the field trip. In general, the feedback questions for instructors should be structured around what can be improved to make the field trip better next time.

Instructors are often numerous at field trips... and experienced. This is a potentially rich, yet untapped source of ideas for improvement!