Assuming you have a child table to orders like "Order items" for each record on each order (which would contain something like the qty sold and $)??
You may need a little code to get your data into the below structure anyway (unless someone can chime in with a native solution).
Assuming you have a structure of Days->Orders->Items, you'd need some way to create records in this table called "Item Sales" which would be a deduplicated list of all items sold in a particular day (across all orders). Once you do that, the below is pretty straightforward; and a valuable technique in general for isolating the max, min, etc.. values in a particular set of data.
I know I left a major piece of this unsolved (getting the data into the above schema) but perhaps try pulling a days worth of item sales, deduplicaing it, and trying the above to see if that's what you need. I'd be happy to walk you through how to do that in a more automated way if you'd like.