Lately I've been having some shoulder "issues" so I go out with as light a bag as possible, often just a couple pieces of paper and a pen in my pocket! On this day I had some sheets of Folio torn to less than 6 x 8 inches. They were perfect for making quick sketches and on one I added some watercolor. When I got home later that day I glued them into my then current journal.
Don't give up sketching because you've got injuries! And if you have injuries, be sensible and carry less. You can still sketch. Think of the big picture—journaling the rest of your life.