Channel your inner Jen with these simple summertime activities.Credit: Celeste SlomanThere are a few things finer in life than having a wide-open schedule, especially in the summertime. Imagine it: How would you spend a completely free summer day? Our July/August cover star, Jennifer Garner, has a few ideas about what she’d do. From coffee on the patio to a nighttime swim with her kids, Garner’s ideal summer day is simple, seasonal, and centered…