there is exactly zero planets or large bodies of any kind - wandering anywhere in space.
None, zilch. You can't move in or out,
There certainly are at least wandering stars and could be wandering planets. Not many.
Encounters between galaxies, between star systems or novas etc cause the existence of Wanderers.
There is also no edge to the "Milky Way" or any other galaxy, they are just less and less dense away from the centre.
While the
Andromeda galaxy (M31) is the nearest galaxy like ours in shape, it's not the nearest galaxy. Ours is about 150,000 LY across (0.15 M LY), some are not much further away.
Some may be close enough to account for wanderers.
List of nearest galaxies - Wikipedia, the free encyclopedia
The satellite galaxies of Andromeda M31 are about 22 to 45 on the list.
There is also the unsolved problems of rotation and expansion which might also account for a few wanderers. Dark Matter and Dark Energy might not be real, they have been hypothesised because the expansion speed of the visible universe is wrong. The rotation of galaxies are "wrong" too. They rotate all of a piece, like a record or any solid disk. The outer bits should be rotating slower than the inner bits due to inverse square law of gravity and most of the mass being toward the centre. So for now "Dark Energy" and "Dark Matter" is the fudge to make the equations work, till either we discover those are real things or some other explanation as to why galaxy scale structures are not behaving in the same manner as individual star systems.
Also interestingly the "dark" bits between the spiral arms of our galaxy have LOADS of stars, just not as many, so they seem darker.
There are about 47 members in our "local" group of Galaxies. Andromeda contains about a million million stars,
at least twice the number of stars in the Milky Way, which is estimated to be 200–400 thousand million. They keep revising the number of stars in our galaxy upwards.
So a few wandering stars, gas giants and rocky planets are to be expected, especially an outer gas giant that survives the nova even of its star.
As Douglas Adams said, "space is big, really big".
Our own star and system is in a local low density "bubble" of the Milky Way due to a super nova. That may have left or caused some wandering objects in the neighbourhood.