Grabbing your package for you is nothing - just a tiny favor.
Tips
history
From Han Yu's 《应科目时与人书》 (Tang dynasty): 「盖一举手一投足之劳也」 - 'merely the effort of raising a hand or taking a step.' Han Yu used it to beg a patron for minor help in his career.
usage
A polite deflection of thanks - if someone thanks you for a small favor, reply 「举手之劳，不用谢」 ('no trouble at all, don't mention it'). Functions like 'it's nothing' in English.
