Final answer:
The sentence contains one vague pronoun, 'they', which could refer to either Squidward's friends or the snacks.
Step-by-step explanation:
The sentence 'Squidward Tentacles's friends are excited for his barbecue this weekend. I think they are planning to bring lots of snacks.' contains one vague pronoun. The pronoun 'they' could refer to either Squidward's friends or the snacks. To clarify the meaning, the sentence could be rewritten to eliminate the vagueness, for example: 'Squidward Tentacles's friends are excited for his barbecue this weekend. I think the friends are planning to bring lots of snacks.'