Shabbat morning kiddush
For some Jews, the kiddush on Shabbat morning is central to Judaism. One mordant observer remarked that single-malt whisky is one of the main forces for cohesion in the North American Jewish community today. So central, indeed, that certain communities started informal kiddush clubs for people who could not wait for the end of the service but slipped out for a quick one during the haftarah, a practice the Orthodox Union tried to outlaw.
Making kiddush on Friday night fulfils the Torah’s command to “remember the Shabbat day”. Kiddush on Shabbat morning was instituted by the rabbis. To have fulfilled the mitzvah of kiddush, you need to eat mezonot, something made with flour, eg crackers or cakes. (Fishballs are not enough, however many of them you eat.)
Otherwise, one should make kiddush again at home before lunch. This is because of the principle that you should make kiddush in the place where you are having your meal (Talmud Pesachim 101a), so kiddush in shul should be at least a little bit of a meal if it is to count as kiddush. But not so much of a meal as to spoil lunch, which is also a mitvzah on Shabbat.