Our pack primarily recruits in the springtime. Summer events they can do include Day Camp (get them shooting BB and archery!), a submarine/baseball game sleepover (alternates every other year), a hike or two, and two other events like a visit to the local trout farm, bicycle derby, etc. In Michigan, you have to capitalize on the warm summer months and get the boys outside!
It also gives new leaders the summer months to figure things out and make the first den meetings in September go more smoothly.