Its funny you should ask this, as I've recently been working on a mentalism routine that can be carried in a wallet. I dont want my pockets weighed down, and dont want to be ensuring that all my props are sorted before I go out just in case someone asks if I can show them something (innuendo thread here I come!).
So far it contains five ESP cards (one with a red back) for a psychological suggestion routine.
One tarot card for another psychological ploy and one ordinary playing card.
Also a few pieces of card. When asked to do something, I have been recently starting with a magic square demonstration using the specs birthdate, from which I show them there lucky number. This lucky number is then used to create a magic square (I dont think this is original to me, maybe berglas, but I'm not sure). Its good to start with a demonstration of a skill that is believable to draw them in, and then go on to the ever more impossible effects. I have started initialing and dating the corner of the card, and people have been keeping it in their wallet. When I first started dabbling in mentalism, I discounted magic squares as mathamatical puzzles, and wondered why it was in 13 steps to start with (I wanted the real stuff...!). Now its an important starting point to what I do.
There is more I will be packing in to it. I was going to include between the lines, but have decided against it (it didnt work the way I wanted for me). The more I work on my own stuff, the less I enjoy using other peoples creations.
As I also mentioned in an earlier thread, I have been working on creating my own stack. I have now devised one that works well for me. Whats important about this stack, is not where all the cards lie (except about 10 of them, but the way the deck is structured. It allows a routine of about 6-8 short effects where the spectator controls the deck most of the time, and shuffles it 2-3 times themselves (even though the routine relies on the stack up until the end), yet all the effects link into a running theme up until the last revelation. Its in its early days yet, but when I leave the house with a deck of cards in my pocket, it will be in that stack from the start.
There is a couple of everyday items that I am investigating that i will wear on me (as are on everyone else) that will allow a nice mental effect. Be this ones a secret!
Went a bit off tangent I think, but the question is something I have been giving a lot of thought to recently. It will be interesting what others carry around with them.