Painting on location especially for beginners can be intimidating. Breaking a scene into vignettes or 'areas of interest' can be a great way to get started. I love to paint like this on location and force myself to 'do something' even if I'm not struck by a 'paintable' scene right away. In fact, this paint NOW mentality can be a great way to overcome artist block... just paint anything, it does not have to be SPECIAL.
As with many painting excursions outdoors, I had a few equipment problems (faulty tripod, wind, shifting light) but this is part of the challenge to maintain focus in spite of difficulty. You'll be glad for the effort, and it feels good just to put paint down! Be present and try even if only for 20 minutes. Remember, sketches don't need to be beautiful to be useful! Not all turn out and this is OK!
The Importance of Simple Studies: Frequent small studies on location increases one's ability to simplify, clarify, and capture the essence of a scene, regardless of your level of painting. See "Fundamentals" for more ideas on how to simplify (in oil and watercolor).
There is no perfect scene. Don't spend lots of time looking for it! Especially with limited time on location. Think of Humble Studies. Or Bits and Pieces. Don't try to take in the whole scene at once. Little studies often lead to bigger things later (back at the studio or for the next outdoor session). The important lesson is to get outside and learn from nature regardless of motivation... as there is always something to extract from the scene. Showing up and going through the motions will get you engaged with your scene and 'lock in' the feelings and atmosphere of the day.