The compression of brittle porous media can lead to the propagation of compaction bands. Although such localization phenomena have been observed in different geometries, including cuboidal and axisymmetric uniaxial compression, the role of boundary geometry on compaction features has yet to be explored, despite its relevance in geological conditions and industrial processes. To this end, we investigate the influence of shaped boundaries and inhomogeneous inclusions in a model brittle material made of puffed rice cereal. Using a variety of geometries, we show that compaction bands assume the shape of nearby boundaries, but return to a default planar form a distance away from them. Remarkably, the band aligns parallel to characteristic lines of minor principal stress obtained from a simple linear elastic model. The compelling correlation between the rotation of the principal stress directions and compaction band orientation holds implications for the geological interpretation of localized patterns in rocks and for comprehending the formation of weak planes in pharmaceutical tablets.