pack a lunch

Meanings

1. Used other than figuratively or idiomatically: see pack, a, lunch: prepare a packed lunch.
2. To be dedicated and well-prepared in pursuing a goal.

Etymology

From the idea that a large and difficult task requires substantial preparation and effort. The same metaphor is at work for get up early; pack a lunch may well have come after get up early as an elaboration of the metaphor. The two phrases are often used in combination, for example, if you're planning to do X, you'd better get up early and pack a lunch.