I only see my grandpa when I visit him in HK or he comes here so I don't have too many ideas. However, my parents are grandparents and even though my niece is only 5...you really see what makes them happy when they spend time with their granddaughter--even if it's nothing "extravagant" or super special. All grandparents want is time
to create memories with their little grandchildren. There's a saying in Chinese that you are hard on your children, but you spoil your grandchildren.
Every Monday the 3 of them go for dimsum and Saturday mornings they go for pancakes. It's a routine my niece has and for a 5 year old..she sticks to this routine every weekend and when it's messed up..she throws a fit because those 2 days are her days with her grandparents. Even though she's so young, I know she will keep this weekly tradition up. (Maybe not dimsum MOndays since she starts K in the fall
Another few things she does with them frequently (if not daily):
-Gardening. She loves "helping" them outside pulling weeds or tossing mini branches into the greenery tub
-Playing soccer or throwing her basketball around in the playroom
-Reading nighttime stories with my dad before bed
-Sitting at our pond feeding the fishies