Grantaire arrived at the party as he arrived anywhere else, already lit. He whistled to himself as he approached, nodding with approval at the living arrangements Musetta had arranged for herself. Nicely done. Grantaire had high hopes for this party.
In a hidden pocket on the inside of his jacket, Grantaire concealed an unmarked dark liquor bottle. For emergencies, he thought with a snicker, and not a moment before.
First plan of action: find Musetta and thank her for the invite. Next? Look for other familiar faces to harass. And then? Drinks... and maybe using them to meet new people. Grantaire wasn't as proficient at this as Courfeyrac, but not socializing in mixed gatherings tended to get him into more trouble than it was worth. Musetta was his friend, and she and Harvey had promised refreshments. That was a good enough reason for him to make an effort.