To the best of your ability, rinse and wash rice. You can use non-purified water as you'll boil the rice later.
Make your sticky rice with a 2:1 water to rice ratio - boil and let simmer. until the top looks dry.
Mix the vinegar and sugar together - stir until sugar is dissolved. Stir the mixture into the cooked rice - but avoid smashing the rice. Allow rice to cool once evenly mixed with vinegar and sugar.
Lay nori over a cutting board (the light, flexible backpacking kind). You can gently went the paper with a (clean!!!!) finger for flexibility. Layer on rice, sliced tomato and cucumber, cream cheese, and fish, then gently roll and slice. Boom. Backcountry sushi.