I do the following, so I'll always have anything I need. If I try to remember each time I go out, it's certain that I'll forget something.

I keep everything that's not camera specific in my photo jacket. That's my Zone VI spotmeter, my Sekonic flash meter (for incident readings), cable release, step up rings (for the Hasselblad), filters (deep yellow, 85B and green), step up adapter for the Artar and lens shade for same. Also various and sundry rolls of film, note pad, a pen, and reciprocity tables. I keep this in the trunk of the car along with my tripod. When I go out I decide which rig(s) (Hasselblad, 4 x 5 or 8 x 10) I want to take and put them in the trunk. In this way I know that no matter which I selected, no essential will have been left behind. When I get to wherever it is I'm going to be shooting, I just don the jacket and I'm ready to go. Since I started doing this I haven't uttered "Oh, DAMN! I forgot whatever...." even once.