महाभूतान्यहङ्कारो बुद्धिरव्यक्तमेव च। इन्द्रियाणि दशैकं च पञ्च चेन्द्रियगोचराः ॥

mahā-bhūtāny ahankāro buddhir avyaktam eva cha indriyāṇi daśhaikaṁ cha pañcha chendriya-gocharāḥ

The great Elements, Individuality, Reason, and also the unmanifested, the ten senses and the one, and the five pastures of the senses;

In plain words: Krishna lists what makes up the Field. It includes the basic elements, the sense of "I," the thinking mind and the hidden source of nature. It also includes the ten senses and organs of action, the mind, and the five kinds of things the senses experience.