Partial homeschooling?

My DS is turning 4 and will likely be enrolled in public school this fall. He will be going to JK full time--although I believe strongly in homeschooling, it is not currently possible in our family. What I mean by "partial" homeschooling is homeschooling just over the summer, in things I think he's going to miss at school. Mainly French, because it's not even offered till grade 1, but I also want to get him started in reading (word recognition), math (recognizing and counting numbers past 10) and continue science/engineering (don't laugh; he's a gearhead and seriously into cars.)

I have some ideas forming in my brain, but I would really like to hear others' ideas for "lessons" at this age, and bounce some of my ideas off you. I think planned-ahead lessons would be best, because I'm pretty lazy and tend to just sit around doing nothing if I don't have a plan for the day.