|Wearing their Target tees and clutching discount autograph books|
Buy the "must-have" Disney souvenirs before you go. If you have little girls, buy them official Disney Princess costumes at a discount store or even at the Disney Store (if high quality is a must) before you leave. You'll spend $20 versus $65-80 per dress and really, do you want your kid wearing a fancy gown in 90 degree weather, while eating a ketchup-covered hot dog? And if it's your thing, rest assured you can bring your own costume to the Bibbidi Bobbiti Boutique and just shell out for hairstyling, makeup and massive amounts of glitter.
You can also buy autograph books ahead of time. I got Disney-branded spiral books that came with a matching pen and a plastic carry case for about $5 on Amazon and my kids didn't notice that their books were any different from the $12 hardbacks sold on site.
T-shirts and other wearables should definitely be purchased ahead of time. You'll see everyone wearing Disney apparel, and even I felt a tug to join the masses (I resisted). But since t-shirts at WDW around $30 a piece, I'm so glad I got the girls their Mickey/Minnie tees at Target for $6.95. Actually, another mom stopped me outside a ride to ask me where I got their shirts, they were that cute. The Disney Store online offers lots of items on sale, including official park merchandise that you won't find at your local Disney Store.
Disney will offer you discounts to prepay for the Disney Photo Pass package, but since the official Disney photographers will graciously take your picture with your camera, you don't need to pay a premium to get everyone in the frame. But go ahead and use the pass while you're there. It's free to have the photos taken and to view and share them online for a limited time.
If your trip is still a few months away, look into applying for the Chase Disney Visa card. I received an application for the card that offered me a $200 Disney gift card, no fee for a year and Disney Dream Dollars (Disney gift card money) on all my purchases, from 1% to 2%. I put our vacation package on the Disney Rewards Visa and used the card for a few months. I ended up with well over $300 (including the original $200 gift card) that I could use for souvenirs (I wasn't a total Scrooge) and tips and wine/beer at our DDP meals.
We saved a little money by bringing the refillable mugs that came with our resort package to the parks to fill with water. But we wasted money on Disney ponchos (definitely something we should have purchase cheaply ahead of time).
I hope someone else finds these tips helpful. As the cast members say, "Have a magical day!"