This article is from the Dr. Pepper FAQ, by Christopher Flaherty with numerous contributions by others.
Thanks to the incredibly hard-working people at The Smoking Gun
(thesmokinggun.com), I can now tell you that the following performers
have specifically requested Dr Pepper by name in the riders of their
contracts, making the beverage a genuine requirement for these acts to
show up at a venue near you:
The Beach Boys
The Bloodhound Gang
Don't you dare take it out of the case!
Joe Cocker, or at least his female vocalists
Kenny G's crew
Diet only--it figures.
Goo Goo Dolls
Exit stage left!
Hootie and the Blowfish
The Neville Brothers
Red Hot Chili Peppers
Peter Tork, of The Monkees
ZZ Top (http://www.thesmokinggun.com/backstagetour/zztop/zztop4.html)
Regular and diet! Well, they are from Texas...
In addition, the late Johnny Cash was also a Pepper.
Maybe that's why he hardly ever sang beer drinking songs.