The phrase "most used-up" implies that something has been completely depleted or exhausted. Antonyms for this term would include words that indicate something is full, abundant, or plentiful. Such words could be "fresh," "unspoiled," "plenty," or "bountiful." Another useful antonym is "untouched," meaning something has not been depleted or impacted in any way. Examples of sentences that utilize these antonyms would include "The fresh produce aisle was filled to capacity with untouchable fruits and vegetables," or "The untouched wilderness was a sight to behold as we hiked through the vast countryside.