Ohhh ... this is a big deal for me. I do a lot of "rough" woodworking. My wife & I build horse stalls, loft, stairs, ... in our horse barn. In the last year or so I too have shifted all my work to square head screws.

My favorite source for screws & hardware - and a favorite for many woodworkers - is:

http://www.mcfeelys.com/

Their web site has pretty well organized guides for selection of the right types of screw - the right finishes for the intended use. I actually bought one of their pre-packaged assortments since I'm always needing different sized screws. The one with drawers - it locks closed so I can carry it out to the barn or whereever. I put the box label in each bin and that makes it easy to reorder as the bin gets low.

By the way, if you have never used an impact driver I HIGHLY recommend them. They are very different from a regular drill. Picture having a screwdriver with a bar that extends off to one side. As you turn the screwdriver a hammer comes down and wacks the bar in the direction of the turn providing extra torque.

At first it seemed to me that this extra torque would make things worse, but apparently since it torques in pulses that allows the bit to seat in between pulses, so even a Phillips screw will do well ... or better.

The impact drivers are so powerful they can actually drive a wood screw clear through wood - head and all .... though in use my 18V Bosch has great control.

No pilot holes unless I'm close to an edge - where splitting is a bigger risk.

Oh, and I hate using the small magnetic driver bits (that I've used with my drill for 20+ years). Now I've switched to the long square head bits with the 1/4" hex base - that latch into the impact driver. The square drive actually holds the screw fairly tightly when starting the screw, and no more bits falling on the ground in between uses. The square head bits last a lot longer than the Phillips heads because they simply do slip/strip, so I'm willing to spend a bit more for them.

By the way, I buy all of my cordless tools reconditioned rather than new. Most don't even have scratches - though I'll soon add them.