Watering plants, getting in the mail and paper. Making sure that there are signs of life in the house that would inhibit someone from wanting to break in. That might include turning lights on and off at certain times. Depending upon how long the homeowners are gone, you should also be turning on water and flushing toilets at least once per day so that the pipes do not emit rusty water when the occupants return.
If they have pets, you would be cleaning up after them (litter boxes, dog piles from the yard, vacuuming up pet hair, etc.) feeding and watering them daily, walking the dog, etc.
While they likely wouldn't expect it, I would also dust to be sure their home looked nice and clean so that they could relax when they got back without having to jump right into chores.
If they have a pool, you might want to clean it out for them. That would include running the filter and vacuuming, unless they have a pool cover. I would also pay attention to weather and decide whether or not their outdoor gardens and lawns need to be watered. If it is winter, you may need to shovel their sidewalks and driveway.