I have a rising 1st grader. :) We do a summer reading program. I have him write down the title of his books (enough writing practice IMO) and every ten he gets a prize(i.e. candy lol).Some other ideas for you:
-starfall.com and http://www.stretchybrain.com/
-legos (seriously these are so educational)
-card games (golf, make tens memory, war (you can also do addition/subtraction war)
-any board game really teaches kids something
-try teaching him a strategy game like chess, checkers, or mancala
-math story books my kids love Sir Cumfrence
-buy a field guide for your area and look up and learn the names of everything you find this summer.
-how to draw books (will keep up the motor skills in a fun way)
-dot to dot/maze books. Amazon has some really neat hard ones if you can't find any locally.
-give him an allowance
-Pick a topic to learn about. Then learn about it in a really fun way. We are learning about the middle ages, doing cool crafts/activies, reading books, day trips ect. The kids are really enjoying it.
-If he isn't into reading try the We read together books or Elephant and Piggie books. Also let him read easier books. I think as parents we tend to push our kids at times. Even if the book is to easy for him it's still practice and he won't be loosing any skills. Green eggs and Ham isn't that hard to read but it is a really long book for a Ker. try alternating pages with him if he is getting tired.
-Books on tape (love these!)