Community Wiki - feel free to add suggestions
In addition to products mentioned in the OP, here are some suggestions from personal experience as a shopper:
Kosher grape juice and kosher wine (made from grapes) are important, as they are typically used for kiddush and havdala.
Full-sized matzo (such as this product, where each matzo wafer is 28 grams), as opposed to bite-sized or cracker-sized (such as this product, where each cracker is 3 grams). It's perfectly fine to stock the latter, as well, but the former can be particularly useful to fulfill the requirement of lechem mishne during Sabbath meals (especially if the shopper doesn't have any kosher challah available).
Prepackaged kosher poultry (such as the Empire brand) would be welcome in the meat section.
Yahrzeit candles, such as the Yehuda brand.
During the Passover shopping season, it is essential to ensure that Kosher for Passover matzo is available (many matzo products are kosher for the rest of the year, but not for Passover). In general, it's important to ensure that products are specifically Kosher for Passover during that time of year.
Other products that are more important during Passover (and which you might want to shelve in a dedicated Passover section, or at least the normal kosher section) include ground walnuts and cinnamon. I also often see salt stocked in the kosher section.
Romaine lettuce1 for maror (or fresh horseradish2 as an alternative) should be available in the produce section before Passover.
1 Ideally certified kosher to ensure an absence of insect infestation - otherwise shoppers will have to go through a painstaking process of cleaning the lettuce at home (although the process is less painstaking if you merely use the stalks). Note that even kosher certified, prepackaged romaine might not be sufficiently reliable in terms of being insect-free. Still, it is almost always either insect-free or nearly so, and is therefore at the very least easier to further clean/inspect/prepare at home.
2 Bottled horseradish (such as Gold's Horseradish) is also a popular product on Passover and year-round. Note, however, that this may not be technically acceptable for maror since it contains vinegar (the mishna disqualifies maror that is "pickled, stewed, or boiled", P'sachim 2:6). Also note that some opinions do not consider horseradish to be acceptable for maror in any form