Problem: You have a lot of things to do. Too many things to do. How can you go to the splash pad, and the pool, and stop at a park, while getting all your housekeeping done and keeping everyone sane? Plus, you've got nap in the middle of the day, and these kids have to eat.
Solution: Pack a lunch. It seems like a pain in the butt when you could just go home and make something, but it makes life so much easier. You don't have to stop what you are doing, and your kids are more likely to eat because they'll want to get back to their fun activities. Plus, a PB and J looks more exotic outside for some reason. And who doesn't love a juice box?
The ten minutes it takes me to pack a small cooler is made up for in spades when we can just open and eat, instead of trekking back home, only to have to make food before we can clean up or sleep or whatever. That would take an hour. Pack a lunch. It's so worth it.