...what food sources can identify in the area I hunt? as far as I can tell there are only two: Oak Acorn Mast (which for the most part is gone now) and grasses.
...JPH you mjentioned hnting early afternoon to sunset...why not the mornings?
I have to qualify my answers with two important points. One, hunting where I do, food sources are easy to find and identify. Acorns, ag. crops and the occasional food plot. Two, I am not much of a late season hunter. But I'll take a stab.
You may be surprised at how many acorns are still out there. They may not be lying in piles like in October, but the deer still visit those trees that produced earlier looking for left-overs. And depending on what kind of weather you've had, the grasses may still produce. If it is still green, I'd hunt over it. One other option may be areas of woody browse. If you have an area of young growth (recovering clear-cut for example) that can also be a good late season food source. If there is snow cover, you can put some miles on and actually find where they are feeding.
As for why afternoon? In the warm months deer move best during the coolest times of day. But in winter, they will often conserve body heat by bedding down in the mornings, but feed during mid-late afternoon.
All this is biased off of what I see around here, so my apologies if this dos not help in NJ.