A pack is a container of something, especially one made of sturdy paper. You might run to the store for a pack of batteries for your new clock and a pack of crayons for your new coloring book.
As a noun, pack might seem like a shortened form of package, but it actually comes from a Germanic root that means "bundle." You can also use this word to mean "group of animals" or "group of criminals," while the verb pack means "fill a bag for a trip." You might pack a pack of cards when you travel across the country by train, since you'll have a lot of hours to fill.