This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
盉 combines 禾 (grain) and 皿 (dish/plate). It likely originally referred to a vessel for grain or a type of container, but the exact historical development is uncertain.
The top 禾 suggests grain, and the bottom 皿 is a dish. Picture a dish filled with grain, but remember that the kanji's meaning is unclear.
For カ, imagine a car (カ) carrying a dish of grain: car -> カ, and the dish 皿 holds the grain 禾.