  After reviewing the variational approach to splitting mean flow and
fluctuation kinetics in the standard Vlasov theory, the same method is applied
to the drift-kinetic equation from Littlejohn's theory of guiding-center
motion. This process sheds a new light on drift-ordered fluid (drift-fluid)
models, whose anisotropic pressure tensor is then considered in detail. In
addition, current drift-fluid models are completed by the insertion of
magnetization terms ensuring momentum conservation. Magnetization currents are
also shown to lead to challenging aspects when drift-fluid models are coupled
to Maxwell's equations for the evolution of the electromagnetic field. In order
to overcome these difficulties, a simplified guiding-center theory is proposed
along with its possible applications to hybrid kinetic-fluid models.
