The current maximum package nickname size is 14 characters, which is very little and I find it hard to fit anything useful in there.
I usually try to put the package's order number in the field.
Sometimes I can fit the order number of the site I ordered the package from, sometimes I can't, and almost 100% of the time I can't fit both the name of the site and the order number in the field, unless I do some creative shortening of numbers and words. This makes it hard to keep up with some of my packages and remember what is inside them.
It would be nice if this could be extended to 28 characters, or perhaps have another field available to type in additional details so you remember what package has in it (that could be viewed when hovering over the package in your mailbox?)