  The conserved charges for $p$-form gauge fields coupled to gravity are
defined using Lagrangian methods. Our expression for the surface charges is
compared with an earlier expression derived using covariant phase space
methods. Additional properties of the surfaces charges are discussed. The proof
of the first law for gauge fields that are regular when pulled-back on the
future horizon is detailed and is shown to be valid on the bifurcation surface
as well. The formalism is applied to black rings with dipole charges and is
also used to provide a definition of energy in plane wave backgrounds.
