Noodles and potatoes tend to be low in protein, but not zero. If you need to add protein, there is always peanut butter.
If you think the protein content will get too low, then add beer. The beer doesn't add any protein, but you won't care.
As for the salt, yes, the commerical food processors tend to put a lot of salt in there to improve the flavor. What you can do is to take one serving of the salty commerical food, then add one serving of noodles or rice. Effectively, that cuts the salt in half.
You probably do not want to cut the salt too low. Backpackers tend to sweat a bit, and that salt needs to be replenished.