To quote Alice Cooper, "School's out for summer!" Now that I've shown my age, let's talk about summer essentials that you definitely don't want to be caught without when running about town with your kids.
I keep a bag packed so all I need to do is grab it and go. First I'll cover the obvious like sunscreen and bug repellant. Of course you should apply sunscreen before heading outdoors but you should definitely take it with you for reapplications. Sun burns are no fun and a sun burn on a child is even worse, so make sure to be prepared.
I always carry a mini first aid kit that contains band aids and alcohol swabs at the very least. I also keep a sewing needle taped to the inside of the kit because my older daughter is prone to getting splinters and we once had to improvise getting one out with a juice box straw....not an ideal situation to be caught in!
You definitely want to keep some non perishable snacks in your on the go bag like granola bars and fruit leather and supplement that with some fresh fruit, cold water and juice boxes when you're ready to hit the road. Pack more than you think you'll need!
I keep a few plastic baggies on hand to hold wet bathing suits and to also protect my phone and camera at the beach.
Now for the fun stuff! I cannot stress enough how important it is to pack a lifetime supply of water balloons. I learned this the hard way upon arriving to the park water balloonless only to see all of the children engaged in an epic water battle. My daughter sullenly walked over to me. I shrugged helplessly, suggesting that she ask someone to share, only to have another child reluctantly hand her one balloon. You don't want your child begging for water balloons, instead, let them be the hero of the playground graciously sharing the stash you brought along. At the end of the season, I buy tons of water balloons when they're marked down for virtually pennies. I know what you're thinking because I've been there. You're thinking about how much you hate tying water balloons every two seconds and killing your poor fingers which are too big to be tying water balloons in the first place. I've got the solution for you! It's the Tie-Not Battle Pump Portable Water Balloon Filler and Tying Station by Kaos. For a measly $10 my child fills the station at the sprinkler and ties her own balloons. We got ours at the local chain drug store but it can also be purchased online. Worth every penny so say my no longer aching fingers.
I also like to keep a jump rope and small ball in the bag. You can pick a few small toys that you know your child likes in case they become bored. I also pack a book for my daughter to read while we're traveling to and from activities so she can keep up with summer reading while still having a fun time.