If you ever rent cars from Hertz, stay at any Marriott family hotels, or use SuperShuttle, or think you will do one of those things before the end of the year, any of those would also earn you miles.
Worst case is paying $28 to buy 1000 miles - probably better off spending the $28 on flowers from 1-800-flowers, as you will keep your account active but also make the recipient happy