In the summer, bring cool, breathable cloting, and sunscreen. Temp's over 100 degrees Farenheit aren't unusual.
In the winter, bring warm, water resistant clothing as rain and damp fog are commonplace, with evening temps regularly in the 30's. Sunscreen in the summer.
Eyedrops (especially if you wear contact lenses...depending on what 'harvesting season' it is, the general air quality can be dry and dusty. If you need special camera batteries, bring a spare--there aren't many places to get unusual types, except for maybe a RadioShack or two.