Pick the park that you plan on being in for NYE and make the reservation at either the 120 day or 60 day mark, whichever is applicable.
Be prepared for a "special" menu (ie: higher priced) on NYE. It's well worth it because the counter service restaurants will be jammed.
On New Year's Day, the parks are D-E-A-D. I would plan a late lunch since you're probably going to exhausted from the day prior.