Enter all of your backpacking equipment into the application by configuring categories. Enter each items Name, Weight (down to the 10th of the ounce/kg) along with a photo of the item. Then, you can create different sets of virtual backpacks. For each virtual backpack, you can add or subtract items from your pack by looking at the name and the photo. As you add items to your backpack, you see the total weight at the bottom of the screen. You can quickly choose the items that will give you the optimal backpack weight.
If your backpack is too heavy, simply remove some items that you feel you can survive without in order to tweak your virtual pack down to that optimal weight for your trip. When you have finished, you can now, gather the equipment up by referring to your list and know for a fact that your pack will be just right for your upcoming adventure.