The other day I found a blooming san pedro cactus - It was over 6 feet tall and had dozens of flowers (mostly closed during the day).
I had just a few minutes but toned paper allows me to paint with gouache very quickly.
Wonderful Nova paper from Stillman & Birn is now my standing choice for the toned paper and I had some black pages tucked with my pocket gouache kit.
Later at home I taped the sketch in my main sketchbook with some washi tape and added a protective layer.
I often add a layer of tracing paper over my gouache sketches because of two reasons: it protects the sketch and also semi-transparent surface allows me to have a second take on the composition or just plain doodle some more over existing sketch - in this case I drew a few flowers with a brush marker.