(dried) boiled rice
餉 centers on dried boiled rice, a preserved food made by boiling and then drying rice.
餉 combines 飠 (food) with 向, which likely contributes the sound and may relate to facing or direction, but the exact historical development is uncertain.
The food radical 飠 on the left shows it's about eating. The right side 向 looks like a container facing you. Imagine dried boiled rice stored in a container, ready to be eaten.
For ショウ, imagine showing (ショウ) someone a container of dried boiled rice: show -> ショウ, and the rice is on display.