I couldn't see a single one. Where are they? There's lots of food because they're mid meal, but I don't see any cups.
Where is your picture? Are you looking at an online resource? If so, then you need to know that the pictures online are very grainy, and frankly not very good. Moreover, the painting is very old, and has been deteriorating rapidly since it was first finished, thus you can't make out a lot of the details of the painting just by looking at a photograph of it, especially if the photograph is published online.
Also, there has been a total restoration of the painting in recent years (I believe it was finished in 1999), a lot of the dirt etc has been removed, so the details are much clearer than they used to be.
For example, Dan Brown makes a big deal out of the fact that there appears to be a disembodied arm holding a knife, but after the restoration it is not clear that the allegedly 'disembodied arm' is actually connected to the apostle Peter, it is 'mysterious' no more.
Bottom line is, if you can't see all the cups, it is probably because you have a poor quality reproduction of it. Find a better picture.