Start calling your relatives to see if they can watch your kids for the day.
When the relatives are unavailable, start calling your neighbors. Hire a babysitter for the first time in years (and the second time ever). Make a mental note that you are seriously ill equipped in the childcare department.
Drive to Maya's and eat breakfast with her boys while she gets ready. Giggle and make jokes and enjoy spending time with children who aren't your own.
Talk, talk, talk, talk all the way to the city.
Pick up Elizabeth and Lauren at their incredibly cool vacation rental (found via vrbo.com), and head to the Mission District. First stop: Curiosity Shoppe.
Meet Derek and buy your kiddos some curiously cool knick-knacks (3-D drawing pad for Aidan and chocolate chip cookie wallet for Avery).
Eat lunch at Gracias Madres. Serious vegan goodness. Go ahead and order a pint of beer to go with your tacos. You don't get out much - you deserve to splurge.
Go to Japantown and experience it Maya-style. She grew up here and knows all the good shops. Buy some printed tape for your kiddos (Lego tape for Aidan and tiny hearts for Avery). Take a picture of the UPS man. Resist buying a stack of Japanese craft books. They're beautiful and inspiring, and you could look at them all day, but you can't read them, and you don't have all day to look at them anyways.
Go back to Elizabeth and Lauren's vacation pad and take some pictures while they put on their hiking boots.
Drive across the Golden Gate bridge and hike up Mount Tamalpais.
Turn around and hike back down when you see two coyotes up ahead on the trail. Make a mental note to come back here with the kids - after all, Mt. Tamalpais is the hotbed for monsters in the Percy Jackson books. This is also the place where Atlas holds up the sky.
Take a blurry picture as you run across the street in Sausalito. Head back to the city, drop off Elizabeth and Lauren at the most visually appealing grocery store you've ever seen, grab a Coke and fries with Maya. Call it dinner. Drive home. Try not to fall asleep. Hug your husband and kids who have waited up for you. Be grateful that they missed you, and that you've had such a great day, you won't need another personal day for months.
Your husband is right, you live a charmed life.