The UV filters offer protection from lens glass scratches. I have been using Hoya filters on all of my lens for years with very nice results. I got the variable contrast ND (had to learn about the variable part) to allow me to shoot at wider apertures in bright sunlight. With the ND filter I can shoot wider and get a shallower dept of field in places like the very bright dump.
All these filters were pretty cheap, the Polaroid variable ND was the most expensive at $45 USD plus shipping.
VIdeo Detailing How Variable ND Filters Work