  We explore the celestial holography proposal for non-trivial asymptotically
flat backgrounds including the Coulomb field of a static and spinning point
charge, their gravitational counterparts described by the Schwarzschild and
Kerr metrics, as well as the Aichelburg-Sexl shockwave and spinning shockwave
geometries and their electromagnetic cousins. We compute celestial two-point
amplitudes on these Kerr-Schild type backgrounds which have the desirable
feature, due to the presence of an external source, that they are non-vanishing
for general operator positions and are not constrained by the kinematic delta
functions of flat space celestial CFT correlators. Of particular interest is
the case of shockwave backgrounds where the two-point scattering amplitude of
massless scalars can be interpreted as a standard CFT three-point correlator
between two massless asymptotic states and a conformal primary shockwave
operator. We furthermore show that the boundary on-shell action for general
backgrounds becomes the generating functional for tree-level correlation
functions in celestial CFT. Finally, we derive (conformal) Faddeev-Kulish
dressings for particle-like backgrounds which remove all infrared divergent
terms in the two-point functions to all orders in perturbation theory.
