Hi there Kelli!
Thanks for popping by the Disney Parks Moms Panel with your great question!
My family splurged on a Polar Patio at Disney's Blizzard Beach Water Park during a recent visit and we loved it! The locker that's included with the Patio is indeed located right inside your 'patio' or cabana-type enclosure. It's a pretty good size to fit many valuables in. Depending on the size of your backpack, you may be able to fit it right inside (I was able to fit a good sized cross body bag and other, loose valuables) or you may consider taking your most valuable items out of the backpack and keeping just those inside the locker. This post on the
Disney Parks Blog from June 2012 shows a photo of the locker.
You are also indeed able to use your Disney Dining Plan with the attendant who takes care of your meal orders that day! It's fantastic. Just be sure to hover around the Patio when you're starting to get hungry so that you can have your orders placed. We were also able to save the 'dessert' portion of our meal to pick up ice cream later (she picked that up too) and there's the option to use Snack Credits for extra 'sides' and more. You'll just provide one of your Key to the World Cards to the attendant and she'll take care of the Dining Plan part for you - bringing you back a receipt showing your remaining entitlements. It's great!
Be sure to arrive early in the day for the best selection of Patios available. My top pick would be Polar Patio #3 if I was able to choose from all of them.
Please don't hesitate to write me back if you have additional questions about your upcoming visit Kelli. I'd love to hear from you again!
Wishing you a simply Magical time at Walt Disney World and a splish-splashingly good time at Blizzard Beach!
Kirsten