This semester we went through chapter 1 of Hatcher (after spending several weeks on point set topology via Munkres) and I had to pick up the group theory I needed as we went along. It was hard, but I made it through and loved the course, so I'll be taking the next course, where I believe we'll be finishing Hatcher. My professor suggests that we'll need to know linear algebra in the form of tensors, but I was hoping to get a more complete list of topics that I can study over winter break.
(Note, there is a similar question here: Algebra prerequisites for Hatcher's Algebraic Topology but its only about the group theory requirements).