The Thirteen-cent Prexie
Third (or fourth) class with other services
If properly paid, this wrapper, sent in May of 1948, could have enclosed a package sent third class, or fourth class under the assumption that it would have been treated as local mail.
If third class, postage would have come to three cents for a two-to-four ounce package, and insurance would have been ten cents for indemnity from $5.01 to $25. If fourth class, local, the package would have weighed from three to five pounds for nine cents postage, plus a one-cent surcharge and three cents for indemnity of $5 or less. If treated as first or second zone parcel post it would have weighed one to two pounds and been one cent overpaid - unlikely use of a thirteen cent stamp, I would think.
I favor the third class interpretation. Judging from the folds in the wrapper, the item was in a relatively small box, and unlikely to weigh two to five pounds.