Now I know that most DBZ fans will be snorting and saying "of course not", because Krillin and Yamcha are two of the biggest punchlines in the programme, but bear with me on this one. Way back in the Sayian Saga, Yamcha and co are killed off pretty quickly, but a matter of weeks[?] later in the Frieza Saga, they have been trained by King Kai and are able to defeat the Ginyu force without much trouble; the same Ginyu force that nearly killed Vegeta, who had enjoyed a couple of Zenkai boosts since fighting Goku. King Kai must be one hell of a training coach to see that much improvement in such a short period of time, and keep in mind that Yamcha and Tien have no innate abilities like the Sayians and Nameks. So when the whole damn universe is on the line against Majin Buu and King Kai has all the warriors of history to call upon, who does he decide to train? Krillin and Yamcha. Two fighters most fans of the programme consider to be nothing more than comic relief.
Admittedly, I'm drawing something of a long bow with this one; I only have a couple of scenes to back up my contention and I'm up against the weight of Krillin and Yamcha's history of defeat. Also, later on in the saga, the pair can't hold a candle to Kid Buu, but that doesn't necessarily invalidate this idea. I like when stories take unexpected turns, and this would have been a hell of a twist. The Sayians and their fusions have been defeated, so King Kai sends in the two most human members of the Z-Fighters to get the job done against an ancient evil that can kill gods? That would have been pretty spectacular. Maybe there's a fan manga or something that explores this possibility, or maybe I'll have to write it.