Both “such as chocolate cake and sandwiches”, and “such as chocolate cakes and sandwiches” would both mean the same thing, and neither one gives any indication about how many kinds of those items are sold (it could be one of each, or many of each). The last one with just the singular “sandwich” doesn’t sound right, and wouldn’t be said by a native speaker, but would be still be understood.... For most nouns, you’d always want to use the plural when saying that a shop sells them (such as the sandwich example). Cake is just a special case here because “cake” can sometimes mean “cakes” in English depending on context.... For example, when going to an event, you might say “they’re going to have cake”, and that could mean they’re going to have one cake, or they’re going to have many cakes.