Assuming you're packing for one person, you'll need about 2.5 pounds of food per day. This includes things like granola, dehydrated meals, oatmeal, ramen noodles, peanut butter, and snacks.
You'll also need to account for the weight of your cookware and fuel. A backpacking stove and fuel weigh about 1 pound total. For a 10 day trip, you'll need about 10 ounces of propane or butane.
So all together, you should plan on packing about 35 pounds of food and gear for a 10 day backpacking trip.