I was initially under the impression that you had to completely "fill" a Prime Pantry box before it could be shipped, but I learned that's not true.
I used one of my $5.99 Prime Pantry shipping credits yesterday. Amazon doesn't carry many of the items I usually buy at the grocery store, but I did get some boxed cereal and a few other things at good prices.
I don't want to order anything else at Amazon until the $1 digital credit returns. So, please post if you notice the credit's changed again.