In a wooden carpenters box I keep the following:
* 8 wooden boards with phillips screws in them
* 8 sets of eye protection goggles (I maintain the rule that when using any tool, we must have eye protection)
* 8 No.2 Stubby Phillips Screwdrivers
Individually you might end up paying $6 each, but I bought a pack 8 of these off of eBay for $17. They are not as desired by most people, so you can usually get them at a good discount.
I took several blocks and predrilled the holes and then I drew arrows so the kids could remember which way to screw them in.
Note: if you have some screws that are difficult to screw in, rub them on a bar of soap and they will go in much easier.