Thanks for asking.

Excluding bonus miles and upgrades eliminates most of the obvious choices.

Beyond that, you can make the in-flight experience better:
- free drink coupons
- free Gogo coupons

Or you can make travel cheaper
- x% off coupon codes
- discount mileage redemptions. I liked the short-haul coach nonstop discounts you used to sometimes offer in the off-season. But how about x% off any mileage redemption, that would appeal to the international premium cabin crowd here too.

As a Gold, any of these would be welcome. For non-elites, you could offer things like the priority boarding package, or free checked bag coupons...