Ice cream containers with lids work well too as the lid contains the smell!In addition to the bucket, sick bags, blue roll and wet wipes. I speak from bitter experience of a clusterchuck.
Sun block and insect repellent. A tick remover if you're in that kind of area.
Good idea!If your school has free sanitary products then its always worth grabbing a few as back up for the students that've forgotten to bring them/need them last minute. It's a small thing to remember, but when you're stuck in the middle of a field with a student who's desperate, and often a little embarrassed, it's a godsend.