chopsticks
筷 centers on the tool used for eating: chopsticks. It is a specific noun with no major abstract extensions.
筷 combines 竹 (bamboo) with 快, which likely contributes the sound. The character refers to bamboo chopsticks.
The top 竹 is bamboo, and the bottom 快 suggests quickness. Picture quick bamboo sticks used as chopsticks.
For カイ, imagine a kite made of bamboo chopsticks: kite -> カイ, and the chopsticks form the frame.