TL;DR: Sleep/rest well, exercise, possibly avoid caffeine, try to put yourself in a good mood.
Sounds good enough to me and probably most coders... I can continue to stick to my 5-8-mugs-a-day habit of 13 years then. My willpower hasn't suffered much I think, although it's hard to tell without some experimental withdrawal period.
And don't even get me started on how much better I feel first thing in the morning, or how I can get through a whole week now without headaches, or how my energy levels don't spike and crash like crazy through the day, or how much better my digestive system feels without all that coffee in it... and what all those things do to one's concentration.
It's insidious as well, because you gradually drink more over time; nobody goes from a standing start to 5-8 mugs a day. If they did, they'd feel like hell. So as you seem to acknowledge, after over a decade you're not even making an informed choice any more; there's not been a single moment in all that time that you haven't either been affected by caffeine or it's temporary withdrawal.