  We provide a well-defined variational principle for 3-dimensional flat space
Einstein gravity by adding one half of the Gibbons-Hawking-York boundary term
to the bulk action. We check the 0-point function, recovering consistency with
thermodynamics of flat space cosmologies. We then apply our result to calculate
the 1-point functions in flat space Einstein gravity for the vacuum and all
flat space cosmologies. The results are compatible with the ones for the zero
mode charges obtained by canonical analysis.
