1. Physical notebook: still using, but some times my notebook is in my backpack/left at home/in office 2. Evernote alike: never works for me. I hate the constant changing features/UI and the overhead of simply opening it 3. (My pick) use instant IM to send messages to myself: the IM tool really doesn't matter. It could be mail app, facebook messenger, slack. Laptop and phone syncing is free and always reliable.
I know these are my throw away thoughts. I am wondering whether there are some amazingly good solutions that I didn't know of. Otherwise I am planning to create one for myself.
Thanks!