You can use flash cards to help your grandson review his addition, subtraction, multiplication, and division facts. These cards can be purchased at learning stores; however, your grandson might enjoy using colorful markers and 3x5 cards to make himself.
On the practical side, let him determine what the change should be at stores and restaurants. Plus, have him figure out the amount of tips that should be paid in restaurants.
One of the secrets of creating an environment that encourages reading is to have your grandson surrounded this summer by material that interests him. Children like magazines because they want to do things in a hurry and the short features can be read quickly. Buy or swap magazines that deal with a wide variety of subjects that appeal to your grandson. Let him subscribe to his favorite magazines so that he looks forward to getting each issue.
Consider enrolling your grandson in a reading program at a library, and you can also go online together to browse summer reading activities. Finally, remember to read to your grandson every day to further stimulate his interest in reading. Try some books from these lists of kid-favorites: