I've made "sushi" ie california rolls on a regular basis in the backcountry.
Heres how I went about doing it: used instant rice, brought rice vinegar in a small dropper bottle, soy sauce packets from the local chineese restaurant, nori, avacado, cheese, kippered snacks, and wasabi powder. I bring a bamboo roller mat as well.
Roll the ingredients and enjoy! You can figure out lots of other ingredients that might work as well...
Its a hoot to have such a treat in camp! I'll never forget the looks on a group as they passed thru, and someone recognized the "makings" of sushi!!
Overall, the weight is not that great considering the punch of calories consumed. Great food is always easier to justify!