What I do is keep a "perpetual" draft page on Blogger! Brilliant, right? If I need to add to the idea list, I can do so any time, just as long as I have internet access. It's especially helpful when we are away from home. Of course, when I don't have internet, I have to do it the old fashioned way, using pen and paper, but the idea is the same.
I like to be able to read on the computer or my phone, so I use a large font and a jot list format for my lists. I do try to organize the ideas so that I can add to them easily. For example, I have separate lists for tutorials, writing topics, quilting topics, tutorial ideas, book reviews, and so on.
An easy way to organize the categories is to change font when I add a new category: as I add spaces or lines, the font follows along. Finally, I use color to help me keep track of new, timely, and used ideas. All I have to do is type using one color then change the words to a second color to show that I've used the idea. Those ideas are still available to help jump-start other ideas and help me remember years later what has been done. A third color reminds me that I need to write about the idea soon.
This system works well for me for a couple of reasons: it's simple, it's available to me anytime and anywhere with the internet, and it's
designed for my needs and can easily change if needed. I could save a document in lots of other web-based places, but having this page on Blogger really makes finding it easy and convenient.
And that reminds me of one more tip: every time I change or add anything--a word, line, space, color--the draft moves to the top of the post list. VERY convenient!