While I lived in Japan, I would often buy little packets of seasoning that were carried in every supermarket. I believe their purpose was for seasoning things like fried rice (チャーハン) and rice balls (お握り). What are these packets called, and is there an easy way to buy them in America? Or better yet, does anyone know how to make them?

The packets were typically salty and had bits of colorful seasoning/particles in it, like nori (海苔) flakes, sesame seeds, spices, etc.