A favorite activity is to grab a magazine or catalogue, and use the products, ads, or anything else inside, to generate designs.
All you need are a few pads of thin, white paper and a black pen.
I also do this at meetings, doctor offices, or even visits with friends: I start to draw based on what I see around me. It is relaxing, conversation inducing, and keeps your inner artist well fed.
These drawings are then scanned, refined, and added to my binders of designs. I can turn them into such useful things as stamps, design papers for collage, and 3D elements to add to paintings.