Will you pack a snack or lunch for him? Why not write him a little note on a post-it to stick on/in his lunch box?
Since he's in preschool, use pictures. I'm sure he'll love his little notes from you. Whether it's a note saying you love him, or a picture of a car or a horse or....a rocket ship? anything at all.
Besides, think of all the time you'll have now to do other things.
That way, you can do your boring errands and stuff while he's in school, and have special time with him after school. Win-win!
Good luck, hang in there.