The sheet also calculates averages where possible for each column. This allows me to calculate expected gas expenses per week, month and year as well as expected number of miles driven
Excel is a nice tool to use for this kind of data logging. To name a few, it lets you place notes in particular cells if there is any more detail to the entry, it's easily modifiable once the formulas are in place, it has more versatility than a web based or phone application, and you can even attach other documents like the owners manual.
You can find a link to the excel sheet by clicking here.