There are endless possibilties.  They can be simply sealed with a clear sealer (like polyurethane) or you could stain it with a wood stain and then seal it.  Many things could be substituted for stain, like watercolors or natural pigments as long as you choose the appropriate sealer (one that doesn't make the stain bleed).  Beyond this charring it with a torch can give a nice look.  A smalll precise torch tip will allow you to be more selective with the effect.  Once burned I recommend a clear sprayed topcoat immediately because handling or brushing will drag the carbon around.  It goes without saying it could be painted but seems ashame to cover all of the wild grain and features.  There are a lot of interesting textured spray paints on the market, however, like the granite look speckled finish.  Another surface treatment would be invest in a woodburning pen and doodle on it as you will.  I have seen hiking staffs that where they write the name of every summit and trail they climbed.  You can even just use a black ballpoint pen and accomplish nice results...just like the old wood school desks I grew up with that had band logos etched into them.  If you want to spend more time on it you could try some chip carving or checkering if you have the appropriate tools and wood species.  A softwood or poplar is easier to carve, whereas a maple would hold checkering better.  You can also use little carbide rotary burrs in a dremel style tool and achieve nice results in many species that would be difficult to carve by hand due to hardness and wild grain directions.  Once roughed in you could lightly chip carve the surface to make it look like it was done by hand.  Once  a surface treatment is done, if it is a staff, you can obviously accessorize it with gems,stones,crystal spheres and so fourth.  Securing them is the hardest part and sometimes choosing a staff with an appropriate cradle makes it easier.  There are also a lot of small battery powered LED harnesses with a switch and remote light that can be recessed in a hole to enhance a cosplay staff.