I have Electric, so I have this little box with compartments, holds some tools, glue, and some parts, then I put that in a larger box that holds a charger, a couple heli's, a covering iron, and some other things. I keep that in the car. When I walk out with my plane, I have the plane and my flight case, which holds the radio, 4 batteries, some cables and the Lipo charger.

So out of this list
1 or 2 new glow plugs
glow plug wrench
glow starter and back-up
prop wrench or c wrench
extra rubber bands or nylon bolts (depending on plane)
fuel and fuel pump
extra props (either the size that you are using or the size range for your plane(s)
needle nose pliers
knife of some sort
3 straight and 3 Phillips screw drivers range from extra small to normal size
starter or chicken stick
something to secure the plane at the field, either a rope and a stake (long screwdriver works) or starting stand
tape to patch any small holes

need only
tape to patch any small holes
extra props (either the size that you are using or the size range for your plane(s)
needle nose pliers
knife of some sort
3 straight and 3 Phillips screw drivers range from extra small to normal size
prop wrench or c wrench
extra rubber bands or nylon bolts (depending on plane)

Although maybe next year I will have a glow or gas model to fly. I will need a bigger box then.