It could be either a Solid - because of the container it would be in- a Liquid - because of the drink itself - or a gas - because of the carbonation within it. - You may need to clarify on which part of the Dr. Pepper you are talking about.
Liquid.
gas
a gas and a liquid cause it can be both
solid
solid.
Gas
solild
It is a rare solid.
soild
solid
Soild
At STP it is a solid