Deadhead

Among the Romans.... The free admission tickets were small ivory death's heads, and specimens of these are to be seen in the Museum of Naples. From this custom, it is stated, that we derive our word “Deadhead,” as denoting one who has a free entrance to places of amusement.

Source: wiktionary

[…] we critics were not his fellow-guests, but simply deadheads whose business it was to "dress the house" and write puffs.

Source: wiktionary

Are you my deadhead to Miami?

Source: wiktionary

With the check came two through tickets—good on the railroad from Hawkeye to Washington via New York—and they were “deadhead” tickets, too, which had been given to Senator Dilworthy by the railway companies. Senators and representatives were paid thousands of dollars by the government for traveling expenses, but they always traveled “deadhead” both ways, and then did as any honorable, high-minded men would naturally do—declined to receive the mileage tendered them by the government. The Senator had plenty of railway passes, and could. easily spare two to Laura—one for herself and one for a male escort.

Source: wiktionary