Crossword puzzle clue "seat without a back"

Seat without a back

Seat whose sitters sit back-to-back

Answer to the riddle "What has rivers without water, forests without trees, and cities without houses?"

"Push 'em back! Push 'em back! Way back!"?

Instrument often used in a flashback...back...back...back... *camera pans up everything goes blurry

Back-to-back-to-back championships

Puts one's seat on a seat, in slang

Subway rider without a seat