Can anyone think of things that there are 8 of?

Answer 1

Fingers on a hominid (not counting the thumbs)

Legs on an arachnid

Sides on a stop sign

Notes to an octave

Grades in a parochial elementary school

and the arms on an octopus

Planets in the solar system

Electrons in a full atomic energy orbit (except the inner first one, which has two)

Seasons of Buffy the Vampire Slayer (counting Season Eight the comic books)

Ages in human history (Paleolithic, Mesolithic, Neolithic, bronze, iron, steel, industrial, nuclear)

"Folds" (moral duties) in the path of Buddhism