When I worked in a larger office (5+ leasing staff), we would obtain gift cards, discount cards, money, etc., as well as "comp cards" (extra 1/2 hour lunch, 1/2 day, etc.) and put them in envelopes (with apartment numbers on them) on a corkboard.
As you received deposits on apartments, you would get to pick the corresponding envelope off the board for your prize!
The apartments that had been vacant longer had better prizes than those that had just come available, but the extra incentive worked to lease more apartments.
We also were able to obtain gift cards from vendors and local businesses, resulting in a low-cost and effective plan to lease more apartments!