how much can you wager in final jeopardy
13, 420, and 911
Jeopardy!
During the break, partitions are placed between the contestant lecterns, and each contestant makes a final wager; they may wager any amount of their earnings, but may not wager certain numbers with connotations that are deemed inappropriate (69, 666, and 1488 are among the forbidden wagers, though 13, 420, and 911 are allowed). 
wiki:826421
Jeopardy! [SEP] Final Jeopardy!
The Final Jeopardy! round features a single clue. At the end of the Double Jeopardy! round, the host announces the Final Jeopardy! category and a commercial break follows. During the break, partitions are placed between the contestant lecterns, and each contestant makes a final wager; they may wager any amount of their earnings, but may not wager certain numbers with connotations that are deemed inappropriate (69, 666, and 1488 are among the forbidden wagers, though 13, 420, and 911 are allowed). Contestants write their wagers using a light pen on an electronic display on their lectern. After the break, the Final Jeopardy! clue is revealed and read by the host.