Whole grain pancakes with maple syrup work best for my body. Too many additives that cause me IBS in the snack bars and most have whey animal protein which is something I avoid - might as well eat bacon.
I have been using a recipe for snack bars that consists of peanut butter and carob powder and honey and rice flour and this has been effective for use while riding over the past 50 years. Many thousands of similar recipes on the Web.