Rice
The main staple of Filipino cuisine is rice.
Almost every Filipino meal has rice as a background for ulam. Salty and sour dishes are not meant to be eaten without the accompaniment of rice. For example, a dish like kare-kare or sinigang would not work if not paired with rice.
Rice is also the basis of many native delicacies. In fact, there is a whole genre of Philippine delicacies called kakanin, whose premise is sweet rice.
Old dictionaries prepared by friars during the Spanish colonial period reveal a vast array of words pertaining to rice. Even today, words such as palay, bigas and kanin are used for differentiating its stages and forms.
Rice is so essential. I wince when I see photos being posted of ulam without rice.