I really got irritated with USPS at Christmas. Apparently Flat Rate automatically includes tracking (I did use the USPS web and prepaid for shipping, and printed the labels myself.) But I sent a small padded envelope, since it was the cheapest way to send. The clerk asked if I wanted tracking, and I said "Sure". I didn't realize until she totaled it and it added about $2.00 to the total. I just let it go. Sadly, it didn't even generate automatic tracking emails to me, like on the Flat Rate shipments ...
I really ought to check out UPS next year, but the Flat Rate service is pretty good for most things we ship.