Vivien has a great detailed lay-out of a well equipped outing. See What to take when sketching plein air.
As well as Katherine's 10 tips for working plein air on Making a mark.
What I'd like to mention and demonstrate, is how much mood influences me, and I suppose all other artists, when I'm outdoors, painting.
...le ruisseau monte...
With the above painting, everything was wrong.
I stepped in a hole when walking down to the river, fell and all my equipment scattered over the place.
I chose midday on a hot day to walk down, thinking I would be in the shade by the river, but I didn't take into acount the long walk down, the heat and sweating which attracted a neat horsefly to sting me, causing an enormous red lump and non stop itchhing and burning.!
At the site I saw the previous day, which then looked perfect, I walked up and down in search for that same perfection. But of course, I was in another day.
During the course of the process, my palette slipped from my hand, falling face down on the ground and it took me a while to get rid of the dirt in the paint. By then, I was way past frustration. But I'm not one giving up easily. That would make me a quitter. I don't mind losing in life, but I hate quitting. So I was determined to finish this painting, which I did.
By the time I walked back to the house(even with Hartman helping me), I was just this side of a corpse. My feet were lead. My ankle hurt from the fall. My head pounded. I was irritated. The sting was burning and aching. Mighty hungry and dead tired. I went to bed and slept. In the middle of the day.
Post mortam came after a shower and good coffee in the welcome coolness from the late afternoon.
*I realized how much mood influences any kind of art making, but especially outdoor painting, where you have a limited time to start and finish a piece. It is a now or never situation. Circumstances will be different tomorrow.
*You don't have the luxury to put away the brush and come back to it later.
*The changing light doesn't leave you any options either.
*And knowing you've gone through all this effort to walk down here(it is hard work to do plein air painting!) adds to the adrenaline of getting the job done.
*I also realized that a scene that looks wonderful today, won't necesary look the same tomorrow.
*It isn't always the most breathtaking scene that ensures a breathtaking painting...on the contrary.
My mood improved and all was well.