Here's a system I've found easy to use and helpful for filing sermon notes on the computer.
1. Have a computer folder for upcoming talks, with a subfolder for each talk and event. Here's mine:
Note that the subfolder names have the date of the event first, in yymmdd format. It used to be yyyymmdd, but I figure I'm not going to be preaching still in the year 2100, so I don't need the first two digits.
That means that if I sort the folders alphabetically, they sort into chronological order, and I can see what's coming up.
I create this folder about once a term, and clear out the old one into my filing system. I find it much easier to keep this folder on a cloud drive, so I can access it from anywhere. I keep all the files related to each talk in the appropriate folder.
2. Have a folder for each book of the Bible. I find a list of 66 quite hard to work with, so I subdivide into genres, then by books, putting a number in front of the book name so that sorting by name also sorts by book order.
For example, the book of Psalms is at Bible/3. Poetry-Wisdom/2. Psalms
3. File notes in the appropriate folder, with a title that looks like this:
Matthew 05v01-16 140621
Having a file title like that means that sorting by name sorts by order within the book, and lets you see immediately when the talk was done as well. Note the importance of trailing zeros – otherwise it would sort Matthew 1, Matthew 15, Matthew 2. In Psalms you need more trailing zeros – so it's Psalm 008 or Psalm 037 because there are more than 100 chapters.
I file notes from sermons that I've preached (still in folders with appropriate files); interesting articles that I've read online; notes I took in lectures in college; notes from talks I've listened to (scanned in), and so on. Here's an example from my folder on John.
4. Show cross-references with shortcuts
One of the beauties of an electronic filing system is that shortcuts are easy to create. If I preached a sermon on Acts 2, for example, that strongly referred to the Tower of Babel, I could create a shortcut to the Acts 2 folder and rename the shortcut as Genesis 11, and file it appropriately.
It makes things really easy to file and to find again. I guess it took a couple of hours to set up in the first place, but it didn't take long to more than recover that time back!