In my case, there really wasn't any change to diet and exercise schedules when I switched to biphasic sleep. I generally eat several small meals per day (rather than a few large ones), and the last meal before the nap is about 2 hours beforehand. I eat again shortly after the nap.
I also avoid caffeine for a few hours before sleeping (either the nap or core sleep), but I've been doing that for ages.
In terms of exercise, mid-afternoon seems to suit me best (if I can schedule things around it - otherwise I take whatever I can get).