Quick, Easy and Efficient Way of Sketching Outside

Mary Kemp - Dead Geraniums
drawing, pen and coloured pencils

I want a way of drawing on the hoof that :
a.doesn't take loads of materials
b.is incredibly quick
c.with a result that is easy to read when I get home
d.and, as a bonus, looks good to the casual bystander.
Not much to ask, but I am working on it !
So far I have been through
pencil, watercolour, pen and wash, watercolour pencils, conte crayons , pastels and coloured pencils.
My latest experiment involves pen, Faber Castells Artists Pen, and Derwent Softcolour pencils.
Here's the picture. Took me ten minutes after lunch.