In the small separately lockable bay behind the curbside rear wheels, I have on the top shelf a small but elongated, red metal (Craftsman) toolbox, with a handle on the hinged lid, in which basic mechanics tools are carried and easily accessed and portaged. Alongside it is an emergency road markers kit, large flashlight, various bungee and other strapping cords, and a few plastic leveling pads for under tires when needed.
On the bay floor below, in the back are stacked 2 small Rubbermaid containers with lids in one of which are air system accessories such as hose, the tire nozzle I built, and a ziplock bag of air fittings. The second box has a pair of lightweight nylon coveralls, gloves, a high power searchlight, and other items. I also have a small black tool satchel in there, up front, in which are bulkier things I more often need, such as an all-purpose Stanley saw that's useful for cutting plastic or wood, a small plastic case with 12v. electric repair parts and stripping pliers, etc., a tube of Lexel sealant, a flexible pickup tool, cans of silicone and WD-40 lubricants, and numerous other small items. Under it all is a small tarp that is not only occasionally handy, it helps keep the other things away from any moisture that sometimes seeps or condenses onto that bay's floor pan.
In another bay I have an assortment of ropes and lines. More than once they were handy in tying up the awning to roof devices when it came loose, and once for tying a bale of barley straw topside.
Inside the coach I keep some basic stuff handy for common interior issues. Included are screwdrivers and pliers of course, and a Craftsman lithium cordless drill-driver kit, a good quality multimeter, a wire tracing tool, containers of screws and small bolts and fastener types, and interior spare parts like light bulbs, cabinet/drawer latches, blind anchors, window vent caps, etc. A small, commonly found Black and Decker kit of bits is handy, especially with its square drive sizes for most coach screws.
As an aside, I also have 6 fire extinguishers scattered around, inside and out. I like the small black, finger-triggered ones I got from Mac the Fire Guy because they fit or can be mounted just about anywhere and are multiuse. I have a couple of large capacity ones as well, and a small one in the toad too. In bays, it was easy to screw a strap of Velcro to a sidewall so it would wrap around a small extinguisher and hold it as and where needed.
Joel