What the heck is a "hot coat in a sack?" (Zager & Evans lyric)

In the song “Cary Lynn Javes” by Zager and Evans - a truly unknown and obscure gem of a song, the B-side to “Mr. Turnkey” - there is this cryptic lyric:
Cary Lynn, Cary Lynn Javes
Do you remember us sitting in the shade?
I gave you a hot coat in a sack
You gave me a flat rock back*

You can hear the whole song here - it begins at exactly 3:00. Unbelievable harmony! Terrific acoustic guitar riff at the beginning of each verse, also. Did anyone actually hear this song when it was first came out?

What is the meaning of that strange phrase about the “hot coat in a sack?”

‘Hop toad,’ aka ‘a frog.’

This song has some pretty evocative imagery. Now compare that to their song ‘Mr. Turnkey,’ in which the girl (who was the victim of criminal assault) is said to be ‘lovelier than oil rights.’