Discover card on file for my cruise- can i pay all the charges at the end with traveler's checks instead?

YES, you can do that and I suggest that you to go the purser's desk when you first get on ship so you know what the process is and then also go settle the majority of your balance well before the end of the cruise. You want to do that because on the last day of the cruise the purser's desk will be swamped with people trying to question charges, correct errors, and settle their bills. Go there and pay in cash or traveler's checks what's on the bill and ask them to put any other charges for the last day on your credit card. You'll save yourself a lot of standing in line.

Yes, you can use Travelers Cheque's to pay at the end of the cruise. Your card is just insurance for the cruise line that you won't leave the ship and not pay. Not a problem at all.

Enjoy your cruise.

Absolutely.

The card on file is just to guarantee payment but the purser can take any kind of payment save for personal checks:)

Yes. Just go to the Purser's office. It's not a problem at all!

you can just leave some travelers checks on deposit at the beginning of your cruise and they will give you the change when you leave.

yes