Prepare my son for Kindergarten

My son will be starting Kindergarten next year, and I can’t seem to get a job at the moment, so we can’t afford pre-school. That means I’m the one who has to make sure he’s ready no matter what. He will be very cooperative one day and a pain in the butt the next when we’re doing workbooks and the like. I’m fairly confident that he’ll be ready when the time comes, but I do worry now and than.