Here is what happened.
(1) I originally mailed it with $0.82 in postage, even though it required only $0.79 ($0.42 + $0.17 for 2nd ounce + $0.20 surcharge because rigid = $0.79). It was a small envelope and less than 1/4-inch thick, so sent "letter" rate

(2) It was returned to me, asking for $0.18 postage due. I don't know why that amount. The only thing I can think of is that $1.00 even is for a 2-ounce first class "flat" (large envelope).

(3) I sent a nice email to the USPO and received a nice speedy reply -- that I should go to the post office, and that they would mail it back to Texas for me -- no charge if I was correct.

(4) I went to the post office today and spoke to a nice immigrant clerk there. She floored me by saying something that has to be totally wrong -- something I never heard from anyone before. She said that because a poker chip was inside, it had to be considered "commercial," and, as such, it had to go first class "parcel" rate, or $1.34 total!!!!

Here are the standards for a first class "letter":
http://pe.usps.com/text/dmm300/101.htm#wp1039555+

More:
2.0 Content Standards for First-Class Mail Letters
2.1 General
With the exception of restricted material as described in 601.8.0, any mailable item may be mailed as First-Class Mail.
http://pe.usps.com/text/dmm300/233.htm

Robert