Food. What do you try to eat frequently that's changed your health for the better?
Preferably, something you make sure to eat regulary when touring.
For me, it's a daily dose of fortified oatmeal with 3 tbls raw honey. No more diverticulities or bronchitis. Make sure I've got both when touring. As a bonus, honey delivers a quick energy wallop when I feel a bonk coming on. Quicker than a Snicker bar.