Choose the correct answer. I _ anything for the party.

The sentence requires the past simple tense to indicate a completed action in the past. Therefore, 'didn't do' is the correct choice to complete the sentence, forming 'I didn't do anything for the party.' This implies that no actions were taken regarding the party in the past. The other options, 'haven't been doing', 'don't do', and 'haven't done', do not fit the context of a simple past action or a general present habit. The correct answer is didn't do.