My guess is that you are on the HAL cruisetour that only has 3 days cruise then you take the land tour from Skagway. The problem with "finding a place to eat" is that the bus stops at a certain restaurant for a meal. You either eat there using the plan or you eat there paying a la carte, which can get expensive. Once you get to places like Denali, you have a few more choices, but as was said, without a car, you are very limited.
Penny's advice is generally good, but I think if you only had two decent meals a day, the meal plan would probably pay for itself. Again, many of the places the cruisetour stops have no options. I read on another forum that someone didn't take the meal plan and later regretted it, for many of the reasons mentioned above.