1. No source control system
2. No bug/issue tracker (or formal software QA)
3. No build automation
4. No dedicated build system
5. No pre-launch checklists
Basically, the latest release was whatever happened to be on one of the engineer's hard drives whenever someone frantically ran in and said "we needed to release!" You can imagine how fun it was to repro when customers reported bugs. And they did, Gandalf, they DID...
Those were the first things to address because they were obvious gaping wounds and I could implement them myself without really having to convince anyone. The CEO thought they were a waste of my time (I hired you to write codes) but didn't actually stop me from setting them up. The next things lacking would take more effort to fix because they were people/process dependent: like no code reviews, no software development process, no bug triage process, etc.