  We have performed photoemission studies of the electronic structure in
LiC$_6$ and KC$_8$, a non-superconducting and a superconducting graphite
intercalation compound, respectively. We have found that the charge transfer
from the intercalant layers to graphene layers is larger in KC$_8$ than in
LiC$_6$, opposite of what might be expected from their chemical composition. We
have also measured the strength of the electron-phonon interaction on the
graphene-derived Fermi surface to carbon derived phonons in both materials and
found that it follows a universal trend where the coupling strength and
superconductivity monotonically increase with the filling of graphene
$\pi^{\ast}$ states. This correlation suggests that both graphene-derived
electrons and graphene-derived phonons are crucial for superconductivity in
graphite intercalation compounds.
