To adequately simulate crew transport, the Dragon 2 should at least carry mass simulators of mass equivalent to that of the astronauts. Will it? Will it be dummies or some useful cargo? Would be a waste if the several hundred kilograms of payload capacity went not used...
1$\begingroup$ I have no information on this, but historically, I know that first flights have carried cargo of the "T-shirts and Tang" variety -- i.e., nice-to-have, but not high-value cargo. $\endgroup$– TristanOct 5, 2018 at 16:05
I saw a presentation by Elon Musk where he said they would be carrying cargo on the demo flight, but cannot find the reference right now.