Have always taken a little cash for incidentals and Mousekeeping tips and rest goes on debit card or KTTW card. If we wind up needing more cash out bank is right around the corner with a ATM.
Travellers Cheques are easily replaced if they go missing which is more than can be said for cash. Next years trip will be my first at a WDW resort (shameful, I know) so I think it'll be some cash and the CC hooked up to my room card.
I only ever use my credit card so I can get points to get free airline tickets. I usually bring about $100 to the parks with me for tips and any stand that does not take a credit card.
Honestly, I don't see the need fro tons of cash or credit cards these days. A ATM/Check card is all I need. I just came back from a 10-day trip, and I think I carried all of $50 the whole time. I mainly used it for tips on the way there and back.
We used to use travelers checks and never had a problem with it. This year we will use cash and debit only.....It is way too tempting to me to use a credit card at Disney!