In brief
The composition helps for the selection, and the division into portions - for the use of the purchase.
Useful to know
When choosing whole wheat bread, check the list of ingredients: Iowa State directs to whole wheat flour first. The dark color or drawing of grains on the packaging does not describe the composition themselves. [1]
For an amount you won't be using anytime soon, the university points to freezing in a well-closed suitable package. Bread for recent use may remain at room temperature according to the product; refrigerated storage may dry it out. [1]
A practical option is to divide the slices into convenient portions before freezing. This is a proposal for organization, not a separate expiration date. Check the label for specific conditions and do not mix "good quality" with a guarantee that each product is fit regardless of its condition. A purchase is more useful when you have a plan for its actual use.
Sources
For further detail and to check the information: