Just remember, in the countries of origin for soy sauce, adding it to rice is a big cultural faux pas. Below is a video focused on Japan, but on the soy sauce thing it applies to other East Asian nations.

Gaijin tip #22: no soy sauce on rice

The video mentions other things you can put on your rice. Furikake is another idea to make your pack food taste better, though it's designed to work with starch only (rice and noodles). There are also a lot of preserved foods in Asian cuisines that survive well without refrigeration, and that is meant to increase your appetite.