About half the time, maybe more, Cul de Sac follows a story arc. The arcs are usually pretty brief and flexible enough that they can change shape or direction without hurting the forward momentum, because there isn't any. It's a luxurious way to work because it can only go wrong by being boring. I like tangents and a daily comic strip is a great way to indulge in tangential thinking; there's always tomorrow to get things back on track (if that's really necessary) so I can keep a loose grip on the reins.
For a little arc like Petey's Playdate, the only thing I have to keep in mind is how long it's going to be and what day a particular strip is going to run. I posted once a while back about what my first rough of a week's strips looks like, and it's pretty unimpressive. But basically, the arc is always divisible by six, or Monday through Saturday, with Monday launching the story and Saturday (a day few people supposedly read the paper) reserved for clean up or commentary. Friday should be the peak of the story, when excitement is at its most white-hot and lives are in the balance. And here it is! All our protagonists and antagonists are in the same room and here comes the flabbergasting plot twist- Alice barging in with all her toys, brandishing her whole gigantic personality like the offensive weapon it is and wearing a hat with a feather in it! This kind of complication might demand another whole week of Petey's Playdate to adequately complete. Or more if Andre starts reading that Diminishing Expectations out loud, with gestures.