Panel 1: A little while after Mike's comment about his being held up by a train, we find John holding a bunch of boxes and apologizing to Elly for being late. When he says that he stopped in at a hobby shop on the way home, Liz interrupts him to ask him what he got.
Panel 2: When he says that he bought himself an electric train, he hopes that she doesn't mind this. This is rather smart of him because he remembers that despite her reassurances otherwise, she'll die being angry about the sports car.
Panel 3: Since she's probably thinking that whatever he bought can fit on a table top and thus be easy to clean up after, she says no and asks him why he thought she would.
Panel 4: When he puts the boxes he was holding on the counter and says "Good! I'll bring in the rest of it!", Elly is gobsmacked because she does not know how much he got and thus does not know how much she is expected to clean up after now.
Summary: This, of course, is the first of many strips in which Elly ends up getting inconvenienced by John's model train fetish. We're in for about eighteen more years of Rod being mocked for being a child thoughtlessly getting in Lynn's way and making Lynn's life harder and exposing Lynn to strange people with strange interests and being more interesting than Lynn is. In the strip itself, this manifests as John's layout being in the way of Elly cleaning the house.