What will be on your oral exam is really up to the examiner. When I took mine just about two weeks ago, about 50% of the material was from the ASA Oral Exam Test Prep book (mostly regulatory type questions), and the rest was discussion on my flight plan, weather charts, and situational/practical application questions. All said and done, my oral exam lasted about an hour and a half. No real surprises here, there were a couple of the questions where you have to list a bunch of stuff that I forgot one or two items on, but I doubt any examiner would fail you because you forgot one item out of a dozen unless it was something important, such as minimum equipment requirements for IFR flight. Particularly if you have done well on the remainder of the oral exam.
For the planned flight, make sure you bring the necessary approach plates, DP and STARs, NOTAMS and Wx for your departure and destination airports. My examiner asked me a few questions about the STAR I filed, and also asked me why I did not file an alternate (not required in my case, just make sure to have the TAF to back it up!)
My practical was just short of two hours. It was pretty straightforward, and there was nothing I was asked to do that I had not practiced many times before. I had one small hiccup on the ILS approach, but I stayed within the PTS, so I didn't bust it. On the partial panel approach (VOR), anything in the cockpit should be fair game for heading reference. Just verify with the examiner before hand that using a backup GPS or the panel mount GPS as a heading reference is OK first. Mine had no problems with it and actually thought it was a good idea to use one when IFR as a safety backup. I was still asked to demonstrate a couple of timed turns (he used them as the clearing turns for the unusual attitudes) just to illustrate I could do them. My holding pattern was part of a GPS approach, so it was really just a matter of flying the prompts on the 430. He did ask me what kind of pattern entry I should use (teardrop in this instance) and what headings I should fly on each leg before I loaded the approach, just to make sure I could do the calculations myself. They're really just looking for proper hold entry and wind correction to keep you in protected airspace. No real surprises, no DME arcs or NDB approaches (airplane is not equipped with an ADF anyway).
Really, it just comes down to being calm, following procedures, and staying ahead of the airplane at all times. When you've got a few extra minutes between tasks, go over what you expect (or have been told to expect) will be next on the agenda. This way you can concentrate on the task at hand and don't have to formulate a plan as you go.