Let F=GF(p^k)$F=\mathrm{GF}\left(p^k\right)$ be any finite field. Let G$G$ be athe group of all affine permutations on F $F$ (i.e. permutations of form ax+b$x\mapsto ax+b$). Then the set of all functions from F$F$ to \bar{F}$\bar{F}$ is a linear representation of G$G$, where g(f)=f(gx)$g(f)(x)=f(gx)$.
What are all sub-representations of this representation? Is it possible to characterize them?
Note: that in this case gcd(|G|,F)$\mathrm{gcd}\left(\left|G\right|,F\right)$ not equal to 1$1$.