My tool bag is a canvas zip up bag, about 5x8x2 and I keep it in a tunnel bag along with a spare quick drive belt. I actually have 3 bags on the tunnel, the Polaris under seat bag for water and food, a roll down water tight powder keg for extra gloves, shirt, socks, first aid kit and then a polaris shovel bag that hold my tools, extra quick drive belt, and extra water.
If you dont want to go the bag route a tool bag can be bungee strapped in several places under the hood. Foot wells have always been a good place to stuff something you dont need all the time. Eric