Gas and electricity average daily consumption both on a timeline and, for gas, cumulative over the year Sep-Jun so that I can see how this year's usage is comparing with previous years. Also average monthly cost.
Produce from the garden (I don't bother with weighing, just add 1 every time a food from our garden features in a meal) - allows me to work out what's best value to grow in terms of contribution to our diet, or which apple trees are showing declining yields and should be replaced.
Anything financial stuff because it's nice to have running totals automatically updated.
My personal jobs list - it's easier to tabulate in Excel than Word, but I'm not really using it for its intended purpose.
Flora list for conservation work I'm involved in - easy to re-sort to produce lists in order of english name, scientific name, flower family, all plants recorded in one area, etc. Would be better in a database program, but Excel is easily available.
Organising volunteer working parties - start by recording which dates volunteers are potentially available, then, having chosen a date, record mileage claims, covert miles to £, add up totals.