The phrase "lose lunch" is a colloquialism that refers to vomiting, typically caused by nausea or illness. Antonyms for this phrase might include words or phrases that relate to feeling well, such as "feel good," "feel fine," or "in good health." Other antonyms might include words that suggest stability, such as "steady," "unwavering," or "firm." Alternatively, antonyms for "lose lunch" might focus on removing oneself from the situation, such as "avoiding sickness," "escaping illness," or "preventing nausea." Whatever the antonym, it is clear that the goal is to feel healthy, stable, and well, rather than experiencing the unpleasantness of nausea or vomiting.