Luis G , Dec 15, 2011; 12:54 p.m.
I could tell you to use what I use, but I'll leave that to others. Intrusion is at least 90% about the vibe you are putting out. The camera is of relatively minor importance. Being anxious triggers into alert status the defense perimeter of others. Relax. You can use your present equipment, and any lens between 24 & 50 (equivalent in FF) to start with (though, yes, anything from a fish-eye to a 1200mm can -- and has -- been used).
Film cameras? My vote would go to any M2 or later Leica with a 35/2 lens (pre-focus, pre-meter and you will discover the significance of lag in fluid situations). Something like an Olympus XA is far smaller, has AE, but a lesser lens and about 1/20th of the price. Load either with some ISO 800 film and have at it.