I typically carry a small amount of cash, and a cc. Prior problems with charging to my room left a bad taste.
With
DDP and assuming no problems, you'll still need to pay a tip, for alcohol, and any non plan extras (not that you'll need any with deluxe dining) at each meal. It can be charged to your room , or you can use cash or cc.
We don't spend much on souvenirs these days, but that part is up to you, and how you'd pay. I think much of the merchandise is way overpriced these days. You COULD spend thousands each day if you wanted. The World Showcase is full of shops with all kinds of international goods.
Otherwise, - tipping isn't supposed to be debated on the DIS- but you may wish to tip bell services, housekeeping, or other services you use. Some folks opt to use a taxi here and there. If you are going between two resorts, it can be much faster than taking two buses.
If you want to use pressed penny or pressed quarter machines, you'll need some cash/change.
I haven't done laundry at WDW in a while!