I'd say carry a gel, but I don't think you'll end up needing it. I always eat complex carbs before a ride, and simple sugars during the ride (because they're more easily metabolized, aka you're able to use them faster). I know you're interested in "before and during" the ride, but I'd say since you're climbing don't forget the protein after finishing (preferably within 20 minutes of finishing) for muscle recovery. Good luck!