Amazon sells Kmart gift cards that could possibly be churned to Disney gift cards in store. You could also order stuff like water and snacks and ship it to the resort or place an order with Amazon Now when you get there.
I have a bunch of Amazon giftcards from my wedding last year, we haven't had a big purchase so we are going to use 1-2 to order snacks and drinks to be sent to our hotel. As others said you could also just buy things you would normally buy in store and put the cash away. I have about $60 in walgreens points so this week I am going to stock up on a few things I need using points and then move the cash over to my Disney Fund (I am cashing in random credits and then will put all together to buy Disney gift cards at Target with my Redcard to pay for meals). This is the closest I get to churning.
if you type in "gift cards" in the Amazon search engine you'll find that there are many gift cards you can buy through Amazon - most notably would be Starbucks which you can then use in the parks
Amazon also sells magazine subscriptions, and usually at really good prices. If there are any magazines you subscribe to, use your Amazon credit to renew them.