The lowly screwdriver, is so basic that it's importance is often overlooked. You may be tempted to buy the cheapest screwdriver set you can find. However, I have learned the importance of a quality screwdriver. Poor screwdrivers tend to cam out and strip the heads of the screws. This doesn't mean you need to spend megabuck on a screwdriver (cough Snap-on cough). But buying a set of 20 for $9.99 isn't a good idea either.
If you purchase a tool kit, it will most likely come with a bit driver set. Bit drivers are useful and offer a wide variety of functions in a small form factor but they don’t exactly serve the same purpose of a good screwdriver set. However if a driver set is what you have to work with, then spend your money on the other basic tools first.
The two most common types of screwdrivers of Flat head (also called slotted) and Phillips head. Not all flat heads and Philips heads are the same. Screwdriver tips are sized just like sockets. For example, Philips heads can be size #1, #2, #4, etc. A #2 Phillips head is the most common. The same goes for flatheads.
Beware, some Japanese motorcycles use JIS (Japanese Industrial Standard) fasteners. These look like Phillips heads at first glance but if you use a Phillips head on a JIS screw, it will cam out and strip the head of the screw. JIS screws are much more shallow cut than standard Phillips heads. Sometimes a JIS screw is identified by a small dot on the screw head, but not always. If you have a Japanese bike and your Phillips head screwdriver or bit just doesn't feel right then it is probably JIS. JIS screwdrivers are hard to find but JIS bits for bit drivers can be had for cheap online.