I had this idea to make a survival in superflat mode, with tekkit, I tried this in vanilla but it was just you running village to village finding loot and not that much fun, but I figured with tekkit you could do so much more...
Heres how I started: I decided that without atleast a useful starter item this would be useless, so I gave myself one of those handheld transmutation tablet (Very handy especially when you got a Klein Star) and a Alchemical tome, since not every resource can be found in superflat (Especially the mod ores like copper and tin). That was all I started with.
Playing: One of the first encounters was a village that was right behind me, it was very lucky that I found some diamonds there, I used 3 of the diamonds for a klein star so i could turn my "Matter" into "Fuel" which was a drawback of the tablet but it works out after the klein star. I then took another diamond and a pair of iron leggings to make a alchemical bag so my stuff would be a bit more secure. I put the rest of the stuff like apples and wheat into my bag and that was about it, I did some stuff later on too like making a talisman of repair and a sapphire sword to kill slimes.
Drawbacks: I think the main problem with superflat is the amount of fricken slimes that spawn... they are just everywhere... I have to reset my difficulty to get rid of them every once in awhile or else theres just way too many. It is really hard to start to focus on tekkit stuff when your playing superflat since it takes quite a while to get started, a blaze rod or bone machine would be very useful for this since you would be able to generate a lot of EMC in very little time... But that is fairly hard to get as you need to get circuits and refined iron for a macerator, and you need 2 condensers and a form of item transport, redpower being more ideal for the purpose. A slime farm could help too since with Rei minimap you can detect slime chunks and make a automated system to kill slimes and pick up their drops.