Yes, they are essential: they provide safety, comfort and stability, allowing the body to completely let go.
Essential kit:

  • 1 bolster (or firm cushion)
  • 4-5 blankets
  • 2 blocks (or books)
  • 1 strap (or belt)
  • 1 chair
  • 1 eye pillow

Until you have specific props, you can substitute them with household items: pillows, towels or books.