My daughters booster is the basic graco with the dual cup holders and whatnot, and it's base measures (roughly) 16x16. I'm sure you could fit a booster behind there, but again even a child is going to have little to no leg room.
No way in hell a rear facing car seat is going to fit without the passenger seat being flipped forward or moved up along way. So you could take the baby with you, but unless mommy is a midget, she would have to walk.
