The Midrash (Bamidbar Rabba, Parashat Korah) relates that David Hamelech instituted the requirement to recite one hundred blessings a day as a remedy to a plague that took place. No fewer than fifty seven of those blessings can be fulfilled if one recites the weekday Amida for Shaharit, Minha and Arvit. On Shabbat, however, there are fewer blessings in each Amida and therefore one must find other ways to complete the requisite amount. As such, the Shulhan Aruch (O.H 290:1) rules that on Shabbat, one should eat many fruits and foods, and smell different aromas so as to be able to recite at least one hundred blessings.
The HIDA (Mahzik Beracha, ibid), citing the Gemara (Menahot 43b), proves that the Shulhan Aruch’s ruling is simply a recommendation but not an obligation. Rabbi Haim Binyamin Pontrimoli (Petah Hadevir O.H 290), uses the same Gemara to show that there is an obligation to have an assortment of foods and smells in order to reach one hundred blessings.
Rabbi Moshe Galanti (Elef Hamagen, 38) suggests that one can make a blessing of HaEtz on an apple, for example, and then have one bring out an orange and recite HaEtz again, and then a date, etc. Thus, rather than one blessing exempting several foods of the same category, one can gain a blessing for each individual food and reach one hundred more quickly. Other authorities including the HIDA (Birke Yosef ibid), however, contend that this would be considered an unnecessary blessing and should not be done.
One custom that developed in the Moroccan community is to recite blessings on olives, salads, nuts and the like between Kiddush and Hamotzi, sometimes referred to as “aperitif”. This custom does not violate the prohibition of an unnecessary blessing and, if done correctly, is Halachically viable way to reach one hundred blessings.
Tangentially, the Rama (O.H. 622:1) writes that on Yom Kippur, the Piyut “En K-Elohenu” is omitted. This Piyut contains twenty verses, each of which is considered a blessing, and was therefore incorporated into the prayers to ensure one could reach one hundred blessings. Since there are five prayers on Yom Kippur, each with multiple blessings, there is no need to recite En K-Elohenu. The Kaf HaHaim (ibid:6) writes that this Piyut is recited everyday, including Yom Kippur, and this is the Sephardic custom.
Summary: One should have an assortment of foods and smells on Shabbat to ensure one reaches one hundred blessings a day. Having an aperitif between Kiddush and Hamotzi is another way to accomplish this.