A friend (recently passed away - cheers out to you, Paul!) was severely diabetic but also a 'hard man' in the classic old skool sense of the term. he always carried his insulin kit, as well as a complete back-up kit (which came in handy when he became semi-comatose after spoiling a batch that got too warm stored in his breast pocket during a climb..)
On the trail and on route, he was religious about checking his levels, often! AND making sure i knew what to do if he went into diabetic shock. Otherwise, he relied on lots of GU and frequent near-candy-bar level trail bars and power gels. I can't stress strongly enough how conservative he was about monitoring his levels.
seemed to work great for 45 years