One of the things that's clear to me from interviews that I've read is that the more popular successful jazz musicians had audiences above and beyond the music community.
If I'm playing in the morning, I'll get some carbs early: porridge with chopped banana. If I'm playing in the afternoon, I'll start with less carbs and have some eggs and fruit for breakfast, then a light lunch about 90 minutes before I play, so I don't feel sluggish or full.