I suggest a beach towel with either his name or his favorite sport or sports team name.
When I worked for a Bernina dealer who also did custom dressmaking and alterations. We made personalized towels for a whole swim team. You could also do duffles or backpacks or even waterbottle holders etc.
Make sure you charge her at least a little more than you are comfortable with. You may find yourself getting into a business you really don't want if you are too reasonable. Good luck.