Get some sort of ACU Molle 3day assault pack. They have waist and shoulder straps, plenty of room, weather resistant, and plenty of room for attachments. The lower end ones, offical surplus not the civvie knockoffs are what you want. 50-70 bucks, id sew reflective materials on but tape would work I guess, and its not a god aweful messanger/fanny bag

And of course with the multiple straps + being army gear its made to sit well and be worn harder. I think you'd be impressed. Hell theres even a id/info clear pocket on the back for emergency info.