This definitely depends on the type of session you need.
For an outdoor session in the summer, I insist you bring water for everyone, possibly a towel to wipe sweat, and maybe bug spray and sunscreen.
For a kids session, I would bring wipes for their noses, a treat to “entice” them to be good! haha!
If you are wearing heels for pictures, you might want to bring something more comfortable to walk to different shooting spots. Bring a scarf or pretty hat to give some images a different look! You’re also welcome to bring props that we can try to incorporate.