Joe,

Sandpaper needs to be automotive if possible (which you can get at walmart or automotive stores) and it is wet/dry.  If you are going to take a piece of sandpaper to a ball there are a few things to know.

1. NEVER use sandpaper on a particle ball.  It will take particles off instead of bringing more to the surface.
2. You always want to wet the ball and sandpaper to reduce the amount of friction between the two surfaces.  
3. Larger grit sandpaper can badly damage a ball, wet or not. (80, 120)

My personal advice is to use Abralon or a scotch brite pad for adjustments.  Even with these a little water never hurts as long as you wipe off the water after you are finished; but water is not absolutely necessary when using these.  If you are using a spinner be sure to continuously turn the ball and hit it from several different angles so that you don't just have a ball that was sanded on two sides.  Hope this helps, good luck with your No Mercy.
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Matthew R. Adams
Current Line-up: Action, Action Packed, The Thing Returns, Vendetta Sniper,  Pure Energy, XXXtreme, and Tropical Storm

Joe,

Those are simply blocks that hold sandpaper disks specially designed for ball resurfacers.  Many people buy them to use by hand, however, because it easily contours to the ball.  Regardless, you could buy one and some sandpaper disks and do everything yourself...even those are wet/dry (up to a point).  If that is the option you think you will be looking at, I would buy everything from 220 and up so as to be able to sand down and back up to desired surface to get rid of any dirt and/or belt marks.  IMO those are more for full-on restoration though, not for a between sets surface adjustments.  I will try to check back soon before heading to league.

Matt
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Matthew R. Adams
Current Line-up: Action, Action Packed, The Thing Returns, Vendetta Sniper,  Pure Energy, XXXtreme, and Tropical Storm

Wow Joe, you are really on top of this and I appreciate that.  THOSE are exactly what you would need for the mid-set adjustments.  Abralon pads are much more expensive than a scotch brite or a package of sandpaper, but they work better and are less harmful on your equipment.  As Daddy always says, "You get what you pay for" and that cliche has never been more true.  If you want full resurface, get the blocks with some sandpaper assortments; if you are wanting small adjustments and minor cleaning, go with abralon.  (That is, of course, onless you can afford to resurface with abralon too, in which case we may need to speak more often...)

Matt
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Matthew R. Adams
Current Line-up: Action, Action Packed, Apex Aggresson, The Thing Returns, Vendetta Sniper,  Pure Energy, XXXtreme, and Tropical Storm