The practical domain for the function f(x) is all whole numbers that are greater than or equal to zero, since the function is defined for any non-negative number of cartons, and cartons can only be purchased in whole numbers.
However, it is important to note that for practical purposes, the domain is limited to those whole numbers that represent a feasible number of cartons that can be purchased, based on the needs and budget of the buyer. For example, it may not be practical to purchase a very large number of cartons of eggs if they will not be consumed before they expire, or if it exceeds the buyer's budget.