I agree with Luanne. Ask a clerk if some things will go on sale later in the week. They usually will let you know if they will. The things that do go on sale later are logo items, t-shirts, some watches and I have seen some liquor specials.
The "best" deals I've found are when ships switch itineraries and they closeout their stock of logo clothing for a particular itinerary such as Alaska. I purchased a couple of NCL hooded sweatshirts for $10 each and my wife bought a decent coat for $30 on our last NCL Alaska cruise. It was the last cruise of the season.
Don't expect any of the high end merchandise to have "last day sales".
I've actually had sales people tell me that something will be going on sale when I've brought it to the register. That is always nice.