My 2 cents on the options... first of all, I ordered premium, S-Line, B&O, and nav
Premium - IMO no A5 should ever be ordered without premium because it's the package that includes the standard HIDs and LED daytime running lights, which kind of define the vehicle's looks. I've never seen an A5 without premium.
S-Line - you get mild lowering springs, upgraded seats, body kit, steering wheel badge, and 19" Y-spoke wheels, all for around $3k. It's a good value: You would spend ~$1500-2000 getting leather-wrapped Recaro Sport seats (like on the Evo), and they wouldn't have power adjustment (the plus being that they are lighter). You would spend about $2-3k getting a polyurethane painted and perfectly fitted body kit. The wheels I don't particularly care for, but they are a good size and decent design to have on the car while you ponder what aftermarket wheels to get. Lowering springs would normally be ~$200 plus another $200 installation. Overall it's a nice overall package to have, and probably helps increase resale value if that's important to you.
B&O - as stated above, it's probably the best bang for the buck you can get out of a stereo. I used to be a total audiophile, and had well over $5-7k worth of DLS and McIntosh components in my previous car. To have a reasonable stereo for $850 is a STEAL. My McIntosh head unit alone was more than this. And you can't beat OEM install in terms of cleanliness.
Navigation - as some members have pointed out, getting nav is pretty crucial because it also comes with some pretty drastic changes to the MMI interface. That should be a big consideratioin whether or not you actually intend to use the navigational part of it. Plus navigation is priceless even if you only use it once in a while.
Technology Package - here's where I decided to say no. It's about another $2.5-3k (I forgot actual price), and the only feature I think I actually feel is a necessity is the Advance Key, which gives you the radio transmitting key fob and push-button start. If this were a standalone option, I'd just get the Advance Key. Everything else like back-up camera, side-assist, and adaptive headlights are luxuries that I wouldn't really miss, but obviously that's a matter of opinion. My Supra has much worse blind spots than the A5, so side-assist is not something I need, and for the same reason, I'm already accustomed to parallel parking a big coupe with big blind spots, so I don't really think the backup camera is absolutely necessary. These are all nice things to have, but questionable whether it's worth the ~$3k pricetag.
-Ray