Final answer:
The correct punctuation for the sentence is the em dash (—) before 'namely' and the commas (,) to separate the items in the list.
Step-by-step explanation:
They were missing a few things on their camping trip—namely, they forgot sunscreen, towels, and firewood.
The correct punctuation for the sentence is the em dash (—) before 'namely' and the commas (,) to separate the items in the list.
Learn more about Punctuation in English sentences