Visible crew/equipment: In the bathroom stall scene when Elvis is examining the hieroglyphics, a mic can be seen in the window reflection when the camera shot is looking out of the stall at Jack the old man.
Revealing mistake: When the coroners are taking Kemosabe's body to the hearse, the one who falls over the porch wall is wearing calf padding which can be seen bulging under his pant leg before he falls.
Factual error: During the fight just before Elvis uses the alcohol, Bubba Ho-tep exclaims a series of Egyptian hieroglyphs which are translated as "By the unwinking eye of Ra." The symbol on the far right is not the Eye of Ra (which faces right) but the Eye of Thoth (an identical symbol which faces left). (01:18:10)
Chosen answer: There's no significance I can find anywhere for the number "AZN-700" - it's just a fake plate they used twice due to the limited budget, and its repeated use is a mistake.