When I go vintage/second hand shopping I always look for art books. This was a real bargain, 10 sek I think (less than 1 euro).
There's one section about outdoor painting. The text wasn't that special, they were mostly talking about packing light by only bringing the most necessary colors, but reading about painting outside made me want to do that straight away :) I am at a stage where I have to be inside right now, but as soon as I am finished with the first layer I might give it a go on the balcony...or even on the grass! At least I've been on an outdoor walk with the puppy today, and I picked some wild flowers for the kitchen.
Other sections in the book were really good! Like this one about pigments and safety. Since some colors are poisonous you are advised to use thin rubber gloves, or a special hand lotion which is supposed to keep the color from penetrating the skin. I have to google that hand lotion and see where they sell it.