Antonyms of "full to the gills" include "empty," "bare," "incomplete," or "underutilized," and "spacious." These terms represent the opposite of a filled or packed space, indicating a lack of abundance or capacity. For example, if a container is "empty," it contains no material, and if a room is "spacious," it has plenty of room to move around. Such antonyms are often used to describe things like containers, rooms, or schedules. In conclusion, "full to the gills" antonyms serve as useful language tools for providing contrast and highlighting different levels of capacity in various contexts.