  We show that there exist infinitely many pairwise distinct non-closed
G_2-manifolds (some of which have holonomy full G_2) such that they admit
co-oriented contact structures and have co-oriented contact submanifolds which
are also associative. Along the way, we prove that there exists a tubular
neighborhood N of every orientable three-submanifold Y of an orientable
seven-manifold with spin structure such that for every co-oriented contact
structure on Y, N admits a co-oriented contact structure such that Y is a
contact submanifold of N. Moreover, we construct infinitely many pairwise
distinct non-closed seven-manifolds with spin structures which admit
co-oriented contact structures and retract onto co-oriented contact
submanifolds of co-dimension four.
