Jjin Mandu is a Korean version of potstickers and very similar to the Japanese gyoza. There are many variations of fillings which you can customise. You can add kimchi, cheese or even truffle if you are feeling extravagant.
Onigiri is a triangle shaped sushi wrapped in Japanese seaweed. Onigiri is my favourite food to pack for work lunch, road trips and picnic. You can actually make onigiri a day in advance and just pack them in your bento lunch.
Gimbap is a korean style sushi roll where gim means seaweed and bap means rice. It is very different from the Japanese sushi because Gimbap uses only sesame oil and salt to season its rice while Japanese sushi uses sugar, salt and vingar.