Words related to holidays
This is the most tempting wrong path. 'Labor' (Labor Day) and 'New Year's' (New Year's Day) strongly suggest holidays. However, 'Boxing' only works if you assume 'Boxing Day', and 'May' only works as 'May Day', which is less common. The theme breaks because the clues are parts of a phrase, not standalone holidays, and it fails to account for the structural relationship.