Early morning buses start by 6:30...they are there for express purpose of getting guests to those meals before the parks open.
Getting to resort meals can be a bit tougher though. If you are going to CM's you may be able to get dropped at the CR. I ask the driver, when I board the MK bus (usually prior to 7:15) which is faster to the CR...walking or the monorail. That way, the driver can make the offer of dropping us right there..and it will seem like he is being 'magical'. I have never asked to be dropped there though. I don't like to appear to be demanding.
If going to the Polynesian or GF you are better off just taking the boat or monorail from MK.
Headed to Boma? Take the AK bus and then transfer to the AKL bus. Again, you can ask the driver, when you get on at your resort, how long it will take to get to AKL from AK...that way, you may get dropped at AKL, rather than having to make a transfer.
Headed to an Epcot resort for breakfast? Take the early bus to DHS and then walk to the resort you are headed to. The boats don't run as early as the buses do...the walk should take about 20 mins....tops.