Years ago I took a tip from (the admittedly fictional) Mr. Sherlock Holmes: I never go anywhere without my small notebook and a pen. Back pocket for notebook (and yeah, the current one is 3/4 full and beat to hell) and pen in front pocket(preferably a black Pilot Precise V5, which is both cheap and high quality).

It's really impossible to express how many times a day this comes in handy. The most mundane information usually, for me, is also the most forgettable, and a quick jot fixes that.

And finally, when the thing is cashed, though most of the notations within are completely useless after a couple days, the object itself has, through wear and abuse, become a compelling and aesthetically pleasing artifact.