Hyperconjugation involves electron delocalization from filled orbitals to empty ones. The tert-butyl cation is stabilized by donation from filled σ C-H bonds to the empty p orbital (σ→π*). 2-butene shows hyperconjugation where filled σ C-H bonds donate to the empty π* antibonding orbital (σ→π*).

Thus, the correct description is: $\sigma \to {\pi }^{*}$ (filled to empty) for both.

Final answer: $\sigma \to {\pi }^{*}$ and $\sigma \to {\pi }^{*}$ electron delocalisations