If you are like a lot of people I know, you get the occasional idea for a product or brand and then you go out to a domain registrar and buy a good domain name if it is available. But of course, making that idea into a reality takes more time than domain registrattion, so it just sits out there, costing you a few bucks a year and teasing the back of your mind.
I suggest that you do a website audit and put up at least one page on your domain as soon as you can, even if you cannot get around to doing anything with it for a long time. And if it is not too much trouble, link to the site from one source that is indexed by Google. Maybe it is your personal blog, or maybe it is another old website.
Why should you take time to do this?
First, it takes a while for search engines to respect a new website. If you have a one page website up, it is better than nothing. It means when you do launch the site you will get much better and faster results.
Second, you can set up your one page website to either promote other things you are doing or even affiliate products. You might be able to cover the cost of the domain, at least.
If you are not a web person, it is OK. This can be the simplest of websites and you can use a template (but with unique content) on each domain name.
I had one domain that just sat out there for many years doing nothing for me, but when the time came and I used it for something, it got ranked so fast and so easily that it surprised even me.
My new rule for myself is that I do not buy a domain without setting up a basic article on the domain’s main page to begin with. The investment is worth it when you try to do something with the domain in the future.
Do a website audit. How many of your domains do not even have a one page website on them? Take some time and get that fixed. It will pay off.