Gum bichromate smeared on a sheet of glass
Seriously, any decent B&W film will do to start with - HP5 or FP4 for Ilford fans, Plus-X or Tri-X for Yellow Box fans.
Ilfords XP-2 can also be used if you want the ease of a C-41 process.
The trick is the processing of the film - over and under development will do all sorts of intersting things.
Remember that older films were less sensitive to different colours - blue in particular was always a problem, so use different filters to simulate this. Study old images and try to work out how they were taken, the poses used, props and settings etc.
The mistake many photographers make is to forget
how the photograph would be taken - forget action shots as the emulsions of the day didn't allow fast shutter speeds even if the equipment had been available to do this.
Narrow apertures and slow shutter speeds - lots of vignetting - not just darker, but OOF to simulate the lenses' defects and chromatic abberations - use the gaussian blur in Photoshop to achieve this, or the RAW interface 'advanced' settings. They allow you to simulate differnet lens types and vignetting effects.
Best of all, make a 'pinhole-type' camera and buy a simple lens from a 2nd hand shop.
And have fun.