Just want to muddy this a bit Bob. Cost accounting (even though it is a necessity), if not interpreted correctly can force managers to make wrong decisions. And most of the time the problem is the allocation of costs to products sold. I remember management consultants, who used to carry around little cards in their pockets with information regarding cutting prices on products. It went something like this....did you know that if you are making 4% profit and you cut your prices 10 percent, you would have to increase sales x% to make the same amount of profit. I'm not saying the information was wrong....but I think it ends up being the wrong way to look at things.
There is a term called "contribution Margin"....I think this is the "ideal" term and the "ideal" concept to learn if you really want to understand business. The contribution margin is the amount of money left when you subtract totally variable costs from sales. In a pizza business, the totally variable costs are food and maybe boxes. So, the contribution margin "contributes" to the payment of all of your fixed costs and ultimately (hopefully?) a profit. The reason that this is important to understand (in my opinion), is because it let's you know how valuable one more sale is, or it let's you know how much a lost sale harms the bottom line. Every sale you make or lose affects the bottom line (in one way or another) by the contribution margin amount.
In regards to finding your most profitable product, it is not enough to know what the contribution margin of each product is....there is another factor..time. For instance, a cheese pizza will have a different contribution margin than a loaded pizza....but which is most profitable.....how about figuring out how many cheese pizzas you can make and bake in an hour in comparison to the number of loaded pizzas and then checking the contribution margin per hour per product. By knowing these kinds of things, you will know for instance which product to discount to increase sales.
Also Bob, if you can get a handle on what your fixed costs are and you know what your contribution margin is, it is simple math to figure out how much sales you need to break even.
The hard part is figuring who your customers are, and knowing why they will buy from you....and how much will they pay.