I always keep at least water with me on trips that are going to last for more than a short errand, meaning that if you're taking your bird with you to run a quick errand, like to a store or something, then okay, but if you are packing him up in a carrier to go for a hike or a road trip, then I don't care how long you are PLANNING to be, you absolutely must take water with you. Period. Obviously in the summer and the hot days of the spring and fall this should be automatic anyway, but I can't imagine taking one of my guys out for a hike, a walk, a road trip, etc. and not having at least some bottled water for them.
I tend to use the Aviator Harness if I'm taking my Senegal, Quaker, or Green Cheek on a walk/hike, bike ride, etc. and use the carrier for longer car rides, but either way I at the very least have bottled water. My bird carrier has a ferret/rabbit water bottle hanging on it's inside so they can get water whenever they want, and if I'm using the Aviator Harness for a hike/walk/bike ride, I keep bottled water in my pack, and usually some fresh fruit, veggies, granola, nuts, etc. for me and them in both situations. But you must always have water for them, as Sailboat said a 10-minute trip can quickly turn into a much longer trip for any number of reasons, and then you're in trouble...