We're at the Swan right now and took the breakfast offer as we're Marriott Platinum. They give you a voucher for each day (excluding check-in day, but including check-out) for "continental breakfast" at Java or Garden Grove at Swan or Fuel or Fresh at Dolphin (I believe you can use it at any location regardless of whether you're staying at Swan or Dolphin). The voucher can also be used instead as a $20 credit for breakfast.
We've only used it at Java at the Swan so far since it's close and we're avoiding indoor dining if possible - it's covered two breakfast sandwiches for us, but staff said we could also get a "continental breakfast" which consists of two pastries, two yogurts, and two basic coffee/juices.