I like spreadsheets, but oftentimes the data I want to track is awkwardly removed from where I want to review it. Take tracking your gas mileage. You have to write it down, do the calculations, then if you want to see what it was over a month, etc. You can see how it gets to be a pain. No more and it won't cost you a dime.
Create a Google form and then use your mobile web-enabled phone to enter data wherever you're at. Because Google let's you decide which columns to make public, there's no risk of showing what you may want to keep secret. Behind the scenes you can have your spreadsheet constantly calculating and you can see your analysis when you choose with no big labor investment.
Sometimes, the simplest solutions are right under your nose.