Question

i know i could not afford caviar,but i could not very well tell her that.(pick out the modal auxiliary from the sentences and state it's function)​

Answer 1

Could-modal auxilary denoting Capacity/ability.

The modal auixilary 'could' is used to indicate capacity or ability.

Answer 2

Question tags are usually get attached at the end of every interrogative sentences. If the sentence signifies positive we tend to add negative question tags, on the other way round if the sentence is negative in nature we add positive question tags.

Surprisingly the same auxiliary verb has been added along with the question tag that has been used at the beginning of the sentence. Hence the  answer to the  given question is   “I am out of practice, ain't I?”