There are two files on my computer that I use when planning an overnight backpacking trip. I share them with you below.
This first file is a spread sheet I made to calculate your pack weight by adding the totals of each item. A digital scale will be most helpful when using the spreadsheet. The spreadsheet breaks down pack contents by section as well gives totals for base weight, base weight plus consumables, and total skin out weight. Measurements can be added in grams or ounces and will automatically be converted to pounds. I created this spreadsheet myself, but it is heavily based off of Mike Clelland's (Author of Ultralight Backpackin' Tips) spreadsheet which can be found here. I highly recommend picking up a copy of Mike's book. It is a humorous and helpful book with lots of tips on how to lighten your pack. If there is enough interest, I may convert this spreadsheet into a Google doc, but for now, you'll have to settle for the Excel version. Please leave me a comment if you find this spreadsheet useful or if you find any errors or if there is something you think I should add to make it better.
The second file I use is the NW Backpacking Checklist. I copied and revised the list that my club uses. The main thing I changed was adding check-boxes to the list and I made it a little easier to print without the sections being split across pages. Not all items on the checklist will be needed, but it does give a pretty comprehensive view of just about anything you would need. I like to check it once right before I say I am done packing to make sure there is nothing on there I forgot.