So many things to do, and many have already been posted. I won’t repost them, other than I will reemphasize the whole eating thing. There are plenty of $15 theme park hamburgers there, but there are also plenty of restaurants with their own theming. Think for a moment the quick server place at Pandora. Those cheeseburger pods are cute, my kids love them.
People watching is a great sport. There is only a couple of rides I cannot do anymore at Disney, so I will sit and watch people.
You can get a haircut at the MK. Nobody mentioned, but shopping/window shopping are obvious ones. Then again, none of those are free, but could be low cost.
There is just the walking around and looking at things. For example, some interesting things about Liberty Square. The shutters are crooked on purpose. Back in colonial times, people took the hinges from the shutters to melt them down to make projectiles for their guns. They replace the hangers with leather straps, which over time would stretch, thus causing the shutters to sag. There was no such thing as a public bathroom back then, and you will see they do not exist at Disney either. The one in Columbia House is actually “over the boarder” in fantasy land, while the closest ones the other way are just a few feet into Adventure Land. And the walkway is done in such a way as to see that in colonial times, the street was also , shall we say, sewer.
See if you can count the number of lanterns on the real oak tree by Liberty Tree Tavern. Hint, there is one there for each original colony.
The flags within the MK are actually not standard American Flags, missing some stars and/or stripes, so they do not have to be raised and lowered. Obviously, the one on Main Street is an American Flag, and is raised and lowered each day. Which brings us to the Flag Lowering Ceremony, which I believe is done at 5:00 PM each day.
There is looking at all the names in the windows on Main Street. Those are the names of the shell companies that were used to purchase all of the land for Disney World. In hindsight, some are quite funny. M.T. Lott Co. was one of them, Ayefour Corporation was another.