Canned beans (unflavored), could be red, black, garbanzo, or a mix of all of them
Instant brown rice
Pre-mix a vinaigrette of olive or sunflower oil, honey, lemon juice or sulfite-free wine vinegar, a pinch of salt, and whatever herbs you like, and bring along in a tightly sealed plastic jar
When you get there, drain the canned beans and set to soak in the vinaigrette mixture (should soak at least a half hour or so) and prepare the instant rice according to instructions on box. Then mix everything together and let sit for fifteen minutes or so, mixing occasionally to marry the flavors. Serve at room temperature.
Julliened carrots, red and/or green bell peppers, and celery can also be added to soak with the bean/vinaigrette mixture and included with the salad if there is time and it's not too inconvenient.
This dish has complete protein, and if the veggies are added, it makes a complete meal.