(my wife didn't keep good count) atleast 30 cups of coffee!
Good job!
Just count the cups at the start of the day and see how many are left at the end. If you leave the house with 60 paper cups and return with 25, then you know you sold 35. Write it down on a piece of paper left at home if you want or make a note on your phone. This way you don't have to remember it or jot it on a napkin or cup you can't find later because you accidentally used itLOL!
Most sales are going to be one purchase=one paper cup. It's easier to count the random oddball situations than to count the normal situations.
Situations where one order does not equal one cup used:
Customer had his own mug and asked for his coffee to be poured into that. (+1 order beyond tally of cups used).
Customer asked for an extra cup to share the drink with her teen. (-1 order from tally of cups used).
So you only tally any oddball orders. One without a cup or one with an extra cup. If you had both of those examples, the two cancel each other out.