This is tough because each has it's own reason to be at the top.
Cameras? I got my K-3 III this year (with my KP as a supplemental), that really took me to another level in my photography and motivation to get out there and shoot more. But I also picked up a
Ricoh GR III Street Edition which is quite possibly one of the best Street Photography cameras in existence.
Lenses? I managed to end the year with the purchase of a
HD Pentax-D FA 150-450mm F4.5-5.6
I think above all of that, my camera BAG has brought me the most return on investment and overall motivation to shoot more. A good, high quality, bag is a game changer and don't let anyone tell you otherwise, HAHAHAHA!