I can often be found walking along the seafront with a plastic bag full of bits of things the cats may like to sniff and play with. Bird feathers, seaweed, bottle tops, driftwood, pebbles. I saw a friend once and he asked what I was doing and he thought I was mad. I also bring them things back when I go up to the horse rescue place where I volunteer.
I must say half the time they give it a quick sniff and wander off so not sure if I'm wasting my time.