If there's one word I've seen that really maters in this thread, it's "balance."
About me: 41 year old type 1 diabetic, into backpacking, hunting, fishing, cycling, running, snowboarding, skiing, (AT, no tele yet) snowshoeing... I've been on a pump since 2003, and on a continuous glucose monitor since 2010.
For backpacking, I don't bonk like I do running or cycling, so I don't rely as much on gels. (although I really like the honey stinger if I do need it) The only time I do need that is if my heart rate is in excess of 150 for a long time. (hard climbing or high elevation) Times with a pack coming to mind involve packing an elk out of a wilderness area 6 miles from the car and getting 2 trips in a day. For that day, it was a gel.
Here are a few tidbits I know, random, but useful (maybe?):
1. Explorers in Antarctica live mostly on FAT (they're likely not diabetics?) I remember reading an article saying that heavy reliance is put on olive oil. Practical for everyday backpackers, maybe not, and for diabetics who are backpackers, probably not.
2. Don't forget the impact of fat, protein, & fiber on slowing digestion.
3. Timing of consumption impacts how your body works. When your blood glucose is low (below 80) your body burns stored fat. I like staying at 120+ when I'm working hard. Correcting for low blood sugar should be different than supplying food for fuel. I use dextrose (aka Sweet Tarts) if I need, even during exercise with blood diverted away from the digestive tract, it's fully digested in 30 minutes.
4. Type 1 diabetics on insulin pumps have a unique tool to manage, the temporary basal rates. Basal insulin is a constant trickle of insulin that counteracts glucagon released by the liver. This has to be programmed into the pump and modified based on activity. When backpacking, I usually run 60% of normal basal rates. Bolus insulin is administered for carb consumption and to correct for elevated blood sugar. More user calibration and carb counting required.
My best advice is to provide yourself choices and keep track of what works. If you're type II, your management is more flexible and your bonking less severe. Before I knew what I was doing and got on the pump, I had hit blood sugar levels of 17 twice, once elk hunting, the other backcountry snowboarding. Taking shots of long acting insulin and lack of familiarity with adjusting to activity were the prime factors in those mistakes. Carb, protein, and fruit/vegetable with every meal is good advice, better advice is to chose carbs wisely, avoiding refined flour or quickly digested carbs as much as possible. For lows, 15 grams of CHO from Sweet Tarts with water is magic.