I started out as piano player and so am technically a percussionist. Yeah, that's right, a piano is a percussion instrument because the strings are hit by hammers.
There were many times when I was performing that there was "nothing" for me to do during guitar driven songs, so I picked up some hand percussion stuff; shakers, tamborines, wood blocks, etc.
Good cymbals and snares are expensive so try some "ethnic" percussion such as djembes, congas, talking drums and the like. Also think about shakers, tamborines, wood blocks, triangles and other types of orchestral percussion.
For the cymbals and snares haunt the small music stores, and used internet sites as well as pawn shops and "bargain classifieds" type publications. I've found lots of fune stuff dirt cheap. Many people don't know what they have. But be prepared to buy some cymbal polish and expend a little elbow grease.
Oh yeah; since you're a bass player you must know a couple of drummers. Perhaps they can make a few suggestions.