For arcade cabinet work, I would get a pattern cutting bit before I get a flush trim bit (unless you're doing laminate, of course). There's a lot more you can do with a pattern bit than the shorter flush trim bit. Having both is preferable though, as you will find situations where the flush trim bit is better suited.
A slot cutter is really the only other essential bit for just about every cabinet though. Other than that, buy as you need them.