I've now been looking for the perfect solution to the backpack/vest conundrum. I have an IAAF vest, but last year I ordered a surveyor's vest from Ben Meadows that seems to work great. I don't have anything printed on it, but there is good visibility with this vest. There are numerous pockets that can hold my pens, calculator, cell phone, nails, tape, washers, hammer, steel tape, recording pad, thermometers, whistle, compass, headlamp, gloves if needed, and bike repair kit. I can put the things I need to access regularly in the front pockets and the heavy stuff in the oversized back pocket. My calculator and cell phone go on inside pockets of the vest. I've been less likely to drop stuff on the ground for restuffing into a backpack, only to lose it or forget it. I have it in the lime green color, but there is reflective orange and grey tape sewn on. It is canvas, but it does have mesh under the arms. There is the Hi-Viz 600D Surveryor's vest, and a 10-Pocket Convenience, Class 2 Compliance Safety Vest. Either will hold many items.
I had been looking for a backpack that was high visibility with reflective tape. I wonder why there aren't any. They would be great for hikers that get lost or are hiking during hunting season. I would love to have my second rider wearing a High Visibility backpack to hold water, paint, and a measuring wheel.