I would never put a bumper sticker of any kind on my car and I have only seen local yard signs so far.
I'm with ya. I don't do stickers, stick-figure families, magnetic ribbons, or suction cup things. Other than a handful of napkins I keep in the cargo net thing between the driver and passenger seats, there is very little in the way of any sort of 'stuff' in the vehicle.
a) Tire inflater.
b) Umbrella.
c) Raincoat.
d) Magnetic US Mail sign.
e) Magnetic orange hazard strobe.
f) One 'Pinky' Ball.
There are a few other things, Spare fuses, headlamps, cleaning wipes, tire plugs, and one air freshener - but they are all in the glovebox or the drawer under the passenger seat.
I keep the napkins nearby to use as tissues, or (since I have this thing about touching food) they are to wrap whatever I may be eating.