There are two people—they went to the city, and one of them died. The dead person's bag is closed and the living person's bag is open.
What was in the dead person's bag?
This question is most likely a duplicate of this one, so, my answer is
The two of them jumped out of a plane; the person whose parachute deployed survived the fall, but the person whose parachute failed died.
The bags contain
medicine. Both people are highly allergic, and were exposed to an allergen. The guy who survived managed to get to his medicine in time; the guy who died did not.
The bags are
essentially wallets. They contained cash, securities, jewelry, precious metals, and/or whatever. Both people were mugged by armed criminals. The guy who lived opened his bag and turned over the loot; the other guy refused to comply, and was shot. And/or stabbed or bludgeoned to death.