COSO is a key area, not so much in terms of the volume of questions devoted to it but in terms of the depth of your understanding of it. It's not enough to know the components of the frameworks. You also need to know how various control functions fit within the framework. Becker covers this well in Chapter 1. You just have to really study it.
Chapter 2 is a very important chapter, IMO. Know the difference between variable and absorption costing. Know how to calculate equivalent units under both methods presented in Becker. Know how to calculate COGS, COGM, WIP ending inventory, finished goods ending inventory, direct materials costs, direct labor, costs, prime costs, conversion costs … basically everything in Chapter 2, you need to know it. Really focus on the homework questions in Becker for this chapter. Do them over and over again, and write down the steps to solving the problems until you understand exactly how to approach these questions.
Obviously, you need to know how to calculate NPV, IRR, CAPM, and all the other financial analysis stuff in Chapter 3.
As far as IT, terms, processes, and segregation of duties are key.
For economics, you need to know how monetary policy affects the economy (i.e. interest rates, inflation, unemployment), the difference between demand/supply and QUANTITY demanded/supplied. Know what market conditions increase or decrease demand/supply. Know how to calculate marginal propensity to save/consume. Know how changes in exchange rates affect the importing and exporting nations in a trade scenario. Know how to calculate GDP.
As for WC, don't sweat those unless you are a really poor writer.
It's been a month since I took BEC, so that's pretty much all I can say. If you're using Becker, you're going to be fine if you really put in the effort on the homework questions.