弁当 (bentou, with a long "o" sound)
ごちそうさまでした (gotchisosama deshita): for thanking your host after a good meal. This expression is so embedded in Japanese customs that people sometimes say it to themselves at the end of a self-prepared meal.
いただきます (itadakimas): literally "I humbly receive", this expression is typical of the Shinto way of life. The informal prayer shows respect and thankfulness towards the kami (spirits) of nature and the people or animals who contributed to make the food. Say it while joining your hands.
懐石 (kaiseki) or 懐石料理 (kaiseki ryouri): a traditional multi-course meal (often served in Japanese ryokan inns).
海苔 (nori): dark green Japanese type of seaweed, very thin and used in sushi (makisushi or nigirisushi).