Personally I do not like stamping Expiration Dates on my Kits. There is NOTHING in this world to tell you that kit will only be used for 3 days except mass False Beliefs in a Set in stone "Code/System" for survival.

The ONLY things in a kit that will determine Length of "use" is Food Water And Stove Fuel. Of Which You can easily Augment them with Means to Obtain Wood Fuel for fires, Sanitation of water, And Means to Obtain More nourishment.

One Can Argue Hygiene Products can also determine this but there is plenty of natural alternatives one must be willing to turn too in desperation.