Simply 3x-ing COGS might 'work', but you're leaving a lot of money on the table.
> And if you want to know the biggest "free profit" in a restaraunt - it's postmix soft drinks and tea/coffee.
No, soft drinks lose you money because it's often a replacement for more expensive alcoholic drinks. The typical soft drink here is $3, even a $6 beer will net me more gross profit than the total price of the soft drink. That's why craft sodas, kombuchas, home-made mocktails and the like are de rigueur nowadays...
Tea/coffee is 'free profit' in the sense it's usually an addition at the end of the meal and not everyone will order a digestif.
Alcohol also has a big markup, don't get me wrong, but it's not alone. And if you want to know the biggest "free profit" in a restaraunt - it's postmix soft drinks and tea/coffee.