I too have wondered about this. I have found a local store where saltines are usually around $1.00 a box versus the name brand version which are around $2.50 a box. It is out of my way and I don't get there often, so when I do, I try to get a few boxes.
Crackers are often packaged in an inner bag which is plastic and air-tight. Even then, I imagine there is a best eaten by time. I have yet to have any unopened packages seem stale, but I eat them in a few months.
I have not tried any additional packaging strategies, but what about storing them in 5 gallon buckets with sealed lids and oxygen absorbers?