Hello Rod, and welcome to Cruisemates. There are several shops on the Conquest, from jewelry, to gifts, crystal.
Each shop runs specials through out the week, so it is best to read your daily Carnival paper, called the Caper.
If you see something that you really want, ask one of the clerks if this item might go on sale during the week. Most of the time, they don't mind telling you.
I have found that something I wanted, did indeed sale out, and I was left without the chance to purchase it myself.
On the last sea day, before the cruise end, they always put the tee shirts on sale, and those seem to be many, so not much chance of them running out.
I hope this info helps, and have a wonderful cruise.