There are no must-haves. there are only needs and wants and job-specific tools that you must have to satisfy your clients' needs. And we see this same inquiry about ten times each year. You're only going to get a list of stuff people enjoy having or have found they cannot live without because that's what they do. People who insist on using volumetric lighting in most of their projects need Trapcode. People who do lots of high end green screen compositing or lens flares have specific needs for the best tools that do that stuff.
I've been using AE since it was CoSA. I have no need at all for Trapcode's stuff nor anything from Red Giant. I get by just fine with what I've got in the box. Your needs, obviously, should be different. But your purchases must be based on what you need and can market to your clients, not what I think you should have.