Hi there, welcome to the site.
Here is how you can do what you want to customize your lunch.
1. Go a day ahead in your food log so that you have an empty day.
2. Add in each food that you have in your lunch and either write down the nutrition totals or open a new FitDay window so you can look at them for the next step.
3. Click on "Create a Custom Food."
4. Give your lunch a name. Enter the serving size (would be 1 if you usually eat it all).
5. Take the nutrition totals from the day you entered the lunch components into and enter them into the custom food boxes.
6. Save the custom food.
7. When you need to enter it, just look in Custom Foods for it and click.
Some people use a separate recipe builder site to calculate the nutrition of a custom food with many components, so that is an option as well; just Google "recipe builder".
And now that you don't have to be perfect, you can be good.