Ad hoc networks and peer-to-peer systems typically require many users to participate, to leverage the full benefits of the system. In this paper we consider incentives for opportunistic networks. As an example, consider an electronic coupon system, where providers send out coupons, which are passed from user to user. Users receive bonus points for each redemption to encourage participation. We define a general model for such bonus point -based coupon schemes and derive an optimal strategy to allow a user to determine how many bonus points she should ask for when passing the coupon. We also show that our optimal strategy is very robust against all other user strategies, and that there is a strong incentive for users to follow our optimal strategy.