Take a picture of your plans for the day and then make that your lock screen pic. Will save you battery life on your phone as you can access plans just by hitting the home button briefly instead of going all the way into the app.
Take a family picture every day before you head into the park. If you're scrapbooking your trip or creating a photo book, it's a neat way to start each day's photos. Also, (and I don't mean to sound negative - I am a worrier), but if one of your children were to be momentarily lost, having a photo in that day's attire is an easy way to show others what your child looks like.