What you see here are crewmembers chewing qat (as it is called in Somalia) or mirra (as it is called in Kenya). Mirra is or is not a drug, depending on who you're talking with. In any case, it's legal in Kenya and the attitude towards it is extremely accepting, even among highly religious people. It seems to viewed as something as harmless as, say, a shot of espresso.
Mirra comes from a slow-growing tree or shrub that grows well in Northern Kenya. Its use is pervasive in Kenya, Yemen and Somalia. Consumption causes mild euphoria and excitement.
In Lamu I was told that nearly all the men partake (the estimate 90% was tossed out) and that this is why the town is so sleepy in the morning. The plane with the mirra doesn't arrive until 10-11am. Our guide told us that when journalists are arranging interviews, he always tells them to wait until around 11. Then the subjects will be very talkative.
In Kakuma refugee camp, I saw women and men relaxing with a bag of stems during the long hot afternoon.