I am planning on starting mountain climbing in the White Mountains of New Hampshire. How should l prepare as far as what foods to bring and some other items to pack?

bring some buddies in case of trouble. Look up hiking in wikipedia and they will give you a good list of what to bring.

If you a really rock climbing you will need the gear and the knowledge, or an instructor, along.

The Whites r great But the Whites r also deadly . You need to read up on the causes & effects of hypothermia, u need to understand it & u need to carry the proper gear needed to minimize it effects .
Those warning signs as the trail clears timberline advising a hiker to turn back if the weather is bad r there for a good reason. The area above timber in the Whites especially in the Presidentials has some of the worst weather in the world. 75+mph wind velocities r not that unusual
So on ur equipment list going above timber in all seasons is a shell garment, a pile or down parka a hat & high energy food. In addittion trails in the Whites tend to be rocky & often steep & lightweight boots r not the way to go. Get a good no BS medium/heavyweight boot with good mid-sole cushioning & lots of torsional resistance. The ultimate WMNF boot is of course custom made by Peter Limmer & Sons in Intervale NH. In recent years they have developed an off the shelf line made in Norway .If u r in the area u should stop in & check out their shop .
Get in touch with the Appalachian Mountain Club in Pinkham Notch NH.They r a great source of information .
Have fun & be careful up there

Agreed with above.

Also, wake up REALLY early, pack light, travel fast. Plan your route, but know the whole area.

pack light items a correct tent would be advisable and also try some foods in the ration packs that you just add cold water and you may need a first aid kit and a emergency beacon also a sharp knife and flint for making a fire

This book is an excellent reference.

Mr. Danger has given an excellent answer.
A handheld GPS and cell phone are a must have as well.