I don't use UV-block filters because I sometimes work with actinic (UV-violet-blue) light, which is all that early photo emulsions saw. If you are in a windy and dusty, dirty, sandy, muddy or bloody environment, a Skylight filter WILL protect the lens somewhat. Otherwise, don't bother. Always use a lens hood, which provides some physical protection without degrading the image.
Some filters are almost necessary. Yes, a polarizer, maybe two (which together function as a variable Neutral Density filter). A set of ND filters, for long exposures. A graduated ND filter -- half is dark, half is light, just what you need to shoot dark foregrounds against bright backgrounds or vice versa. Those are the basics.
I like spectrum-slicing, using different colors of light. I use violet or blue-violet filters for actinic light, and IR-pass filters for infrared. I use plain old B&W colored filters (red, green, orange, yellow) for certain monochrome effects. And a yellow filter when shooting garish neon-lit darkness in color adds a nice touch.
Be sure to pick up and discard any filter tips you see laying around, eh?