I used an old Jeppesen bag I got for $10. Had one main pocket and a bunch of outside pockets. Inside I had headset, POH, Approach Charts, and Company manual (required). Outside I had a kneeboard with a little pad on it, my charts of planned use, checklist for the flight (items to be taught to standards and introduced), 2 pens, a small flashlight, 5 hour energy, and some instrument covers. That's it. The rest was either on me or I had my student carry it. Every semester I sat down with a student on what I expected them to bring. I usually had a backup in my office, but it was clear that if they didn't have it, we didn't fly. You shouldn't have to baby sit your student on everything. I carry approach charts as they may have them outdated, or we may be in a situation where I need to be the one proficient to land the airplane safely, not them. Remember, you should be comfortable being the PIC when need be, but go ahead and use their stuff if you can, pack yours light.