Over the past 25-odd years I've used text files, Moleskine notebooks I carried with me everywhere and lately just iCloud notes. My main problems turned out to be not the preservation of such ideas, but not actually bothering to write them down often and lack of discipline at revisiting them later. Judging from past "successes", getting to work on good ideas immediately has worked best for me.
Basically the same as me, though I love spending time going back a rereading all my notes. Sometimes I'm really tempted to delete one, as it's stupid, but I resist the urge.
