The correct answers are We don't have any guacamole left! and I bought some extra ice just in case.

As a general rule, we use some in affirmative (positive) sentences ("I bought some extra ice") and any in negative sentences ("We don't have any guacamole").

"I didn't buy some salsa" is incorrect because it is a negative sentence and should use "any." "We have any paper plates" is incorrect because it is an affirmative sentence and should use "some."