If you staying onsite just use your preferred cc'd at the front desk and your room key will give you charging privlidges in all the WDW parks. All the shops/restaurants and even many kiosks will take a cc'd or debit card as well as TC's and, of course, cash! Be sure to have a moderate amount of cash on hand for ice cream/water/soda/etc as some of the carts/kiosks don't take cc'ds.
Generally speaking I take 2 cc'ds - one to leave the # at the front desk and charge with my room key, one for just in case to be locked up in the safe and my bank card for quick cash at the atm, located at every resort and also within every park. Personally I don't use travelers checks as imho they are difficult to obtain and cash so I just hit the ATM a few times each trip and deal with any service charges.
HTH
TJ