Scientific Progress Goes "Boink"
The title noise is that of the duplicator producing copies of Calvin -- who didn't think how copies would act. Also appearing are dreams of waking up, snowballs, floating to the ceiling, and growing enormous.
Attack of the Deranged Mutant Killer Monster Snow Goons
Calvin makes the mistake of bringing a snow man to life. It turns itself into the freaky mutant shape by packing on snow, and obviously can't be hurt by snowballs. It also features chicken pox, the attack of the bike when Calvin tries to ride, and Calvin's ill-fated attempt to kidnap Suzie's doll, since she opts for even retribution.
The Days are Just Packed
An allusion to summer. There are other days, of course, where various ploys do not get him out of homework, the valiant attempt to get the story he is meant to write by time traveling, and a good number of gag-a-day comics.