Notebooks
I pretty much always carry a bag containing two notebooks

1) A diary
2) A moleskine notebook I just write anything that comes into my head down in: doodles, extracts from books, words to look up, things people have mentioned I want to follow up on, etc. Sometimes even things as boring as a to do list.

I use the diary on my email, but it's not the same as having it all in a book in my bag. And the notebooks aren't something I think I could replicate with any sort of technology - paper and pen wins.

EDIT: Ooooo... and I also have an N64 under the bed which I haven't dug out for ages and is probably due an airing if I get any similarly minded visitors: Grenade Launchers on Stack.
(SnowyTheWereRabbit the Leporid from Hell, Sun 7 Nov 2010, 23:53, 3 replies)

I still use a filofax for addresses that I have collected for more than 15 years.
Can't beat the moleskine though for tactile pleasures of thick paper.
(boozehound is drinking your bar dry, Mon 8 Nov 2010, 0:28, closed)

I keep a notebook with me
And if, as happens from time to time, I am in a restaurant and I receive bad service or food, I start jotting on it. This often results in rapid recompense.

But then, I am AA Gill.
(McChinaman banned, Mon 8 Nov 2010, 8:59, closed)

This is quite a nice idea, actually
Must try it sometime and see if the service improves
(SnowyTheWereRabbit the Leporid from Hell, Mon 8 Nov 2010, 9:49, closed)