Following on from Martin's blog about his use of spreadsheets I thought I'd post some thing about my use of the same.
I keep a master kit list that I save as... for each trip and use the saved spreadsheet to build the kit I'll need to take. The master workbook has a kit list sheet, a menu sheet, an action sheet and a master item sheet. The master item sheet lists all the kit I own including items that I wouldn't dream of taking on a backpacking trip these days. The action sheet is just that, a list of bits and bobs that need doing for the trip. Again the menu sheet title says it all really. The kit list is preloaded with default items that I'm likely to be using, along with some occasionally carried optional ones. So depending on the time of year, terrain, weather, etc I'll move stuff around to suit. Along with the very detailed master item list* this helps keep the weight in check. And you can test options and the impact they have on the pack weight.
After the trip I use the spreadsheet as a debriefing document. Each piece of kit gets the three pile treatment on the page. I'll assume you know what I mean by this, so any items that aren't used or only used once go under review or get struck off. Unsurprisingly after only a few trips the amount of stuff that I carried but I didn't need disappeared out of my pack. I make notes on how the kit performed, any lessons learnt, and things to do differently next time.
*The master list detail is very thorough with a view to give maximum accountability of carried weight, this is reflected in the seemingly long list of items on my kit list.