Anything with a bottle opener!
I suspect a lot of guys love rock and roll, but not many have lived with a band. If I was a rocker, my knife would be something that fit with my instrument. So for a lead singer, I'm thinking inlaid sebbie, or something similar, classy but solid. maybe for a punk band instead of the old style stiletto switch, I'm thinking custom emerson. For the guitarist, depends on the ax, a strat guy is going to carry something like a razel, sharp corners and mean, where a tele guy is going to carry something long and slim. A bassist is going to be looking for a big ZT or SOG, like a pentagon2 something that goes bang when the blade lands, maybe an manix2 XL. Drummer is going to carry a multi, since he's gotta be building that kit. but they also carry a stick bag, so I'm thinking a Gerber mk2 in there.
I don't think rockers are going to go for the mall ninja stuff, you spend that much time picking pedals and skins, its about how things work, not what they look like. Those guys pick gear for a reason. Party rockers are going to carry pretty knives, while the punks are going to be looking for weapons. You know those black metal guys all just carry short-swords or smatchets anyway! Grunge rockers might carry more utility sorts of blades, but I'm thinking it would be something like a delica or endura. just something to get the job done. I'll bet Lemmy would have carried a Buck110 for a long time, maybe in one of the fast opening belt sheaths, but I can also see him being a knuckle duster kinda guy. Even theatrical rockers like GWAR might carry something from a Kit Rae catalog, but I wouldn't be surprised if they sprung for live blades. Might look silly, but don't argue with the result. The only band I can see carrying cheap gas station knives is KISS, and only because Gene Simmons would have had his face painted on them! And the Nerd-core guys are carrying Vics and LMs, along with enough LED lights to run half the show!