Like I said, 'baya' has no direct translation in English, however, this is how we would use it in the following situations:
1.) Oh, geez -- baya (So instead of saying 'geez,' you can say 'baya') I guess, we all know when the expression 'geez' is spoken or uttered.
2) A: He ate the bread. A: Gikaon niya ang pan.
B: No, he didn't. B: Wala baya. (Remember that a finished action is negated using "wala")
3) Palit baya og pan para sa pamahaw. (Person A is making sure that person B will not forget the errand.)
Buy bread for breakfast, okay?