"Champing at the bit" is a common idiom used to describe someone who is impatiently waiting to take action. However, there are many synonyms that can be used in place of this phrase. Some examples include: "eagerly awaiting," "anxious to begin," "itching to start," "restless to act," "impatiently anticipating," "fidgeting with excitement," "itching for action," "keenly anticipating," "yearning for opportunity," and "chomping at the bit." Each of these synonyms conveys a similar meaning to "champing at the bit", and can be used effectively to provide more variety and interest to your writing.