The best way to store your ideas is to memorize them. This is the ultimate goal. If they are baked into your consciousness, they become an automatic part of everything you do.

Humans have a long evolved history of memorization. Before we had writing, we had to memorize the things that mattered. Don't forget that this practice is baked into your genes.

To get there, it helps to write down your ideas, and to organize them together, reflect on them, find patterns in them. But the actual medium doesn't matter as much as the practice you follow. Remember that when you are writing down your ideas, you aren't dumping them into an offline store -- you are making them nice and pretty and well-organized for your brain to remember them as you write them down. Write them down to fill in your brain; not to offload.