DUCT TAPE IS THE BEST!!! I read about it in the Unofficial Guide in 1999, have used it ever since. We always pack duct tape for our WDW trips! If I have to be on my feet more than 12 hours at work I use duct tape. My mother uses it, and my husband uses it too! It really is a miracle. Also wearing two pair of socks, one thin and one thick (another tip in the Unofficial Guide) works wonders. I do that on a regular basis now!
If you wear two pair of socks and put duct tape on your feet EVERYDAY at the beginning of the day YOU WILL NOT GET BLISTERS no matter how much walking you do. But I do suggest that you experiment with duct tape before leaving home to get your technique just right. You don't want the duck tape to stick to any toenails, can actually pull of your pinkie toe nail (happened to me!). You don't want to use very large pieces of the tape (it causes too many thick wrinkles and overlaps that could cause a blister). You don't want to use too many small pieces that will come off as your feet start to sweat throughout the day. I always wrap the balls and heels of my feet, almost making a kind of duct tape cast. My husband just uses three pieces: one piece starts at the bottom of his toes and runs to the back of his heel, the next piece goes over the ball of his foot, and the next piece goes around the back of his heel, very, very simple and easy to do! It just makes such a difference.
**By the end of the day, your feet sweat so much that usually the duct tape comes right off when you remove your socks. There's no painful pulling of the skin. If the tape doesn't come right off, just put your feet in hot water and the tape will come off very easily.
If you ever have problems with sore feet or blisters I beg you to try this. It is one of the best (if not, THE BEST) WDW tip EVER! I can't imagine going to WDW (or living life) without duct tape!!!
One tip I've used for packing tape, stands to reason you could use it for duct tape: If you will take a box cutter/knife/razor and cut out the cardboard inside the duct tape roll, you can actually squish the roll into a flat "roll". It will take up a lot less space, so you can pack it in the bag you take into the parks (just in case you need a quick fix), you could even slip it in your pocket, but I don't think that would be necessary, unless you plan on doing some handiman work around the Magic Kingdom.