Rest assured, argel1200, ECB is a complete game. Our playtesting process showed that it achieved our goals of being lightweight, easy to learn, and easy to run, so it's not the kind of game that requires a lot of supplementary material.
If you haven't already, I recommend checking out the ECB quickstart packet. It's a free look at the game with everything you need to play a one shot (or start a campaign, really). In particular, each character sheet has rules references within easy reach. You can find the quickstart here:
https://docs.google.com/spreadsheets/u/2/d/1O_LNk3pV1qVn__n1l1TAVbLkf-ZYK__t4DQT...
Happy gaming!
- Eli