What are some things every man should carry on him at all times?

Based on my own experience:

Absolutely necessary:
Wallet/Card Case
- Cash (Figure about $50-$60 in a good assortment of bills)
- ID/Driver's License
- MetroCard (or equivalent in your city)
- Debit/Credit card
Keys
Cellphone
Chapstick

Less so:
Mp3 player

Totally optional:
Pen + Small notebook (not necessarily a Moleskine, I'm staring at 80pp mini notebook that cost me $.85 that can do the job just as well)
Multitool (Its good to have in your house but my AP US History Teacher is the only person I know who kept one on him and actually used it regularly)
Lighter

Keys, watch, wallet, and cell phone.

as little as possible.
in philadelphia, i just don't need a pocket knife on a regular basis.
cash is king

a thin wallet, containing only one debit card, one credit card, license, 3 business cards, at least $100 cash

iphone

keys

in the car, i do like to have a knife, toothbrush&paste, reusuable water bottle, small backpack, towel and workout clothes

the only things i never leave the house without:

Money clip with some cash & three cards - 1 debit card, 1 prepay credit card & 1 piece ID
Phone
Keys.

Spectacles, testicles, wallet and watch.

wallet with cash ($20 can get you into our out of 90% of stuff)

credit/debit card

knife

cell phone

....if you need any more than that you are probably in a bad situation.

An iPhone, a credit card, and some cash.

I carry-
40 S&W
Pocket Knife
Fingernail clippers
Cash & Card
Flashlight
Blackberry & Charger
Hand Sanitizer
Ipod
Camera
Clif Bar
Gum
All in a maxpedition fatboy.

Cell phone, keys, small pocket knife, lip balm, and wallet (ID, credit cards, debit card, and $20 cash). Keep it simple.

everything greg said but including a phone and a lighter.

Wallet with $50 in mixed bills, debit card, and ID
Watch
Phone
iPod with headphones
Keys

keys

wallet with the following:
$50 or so in mixed bills
debit & credit card
business cards

Lacie Ima key (USB Drive, goes on key ring)

iPhone (serves as phone and ipod)

watch

keys

wallet with the following:
$50 or so in mixed bills
debit & credit card
business cards

Lacie Ima key:http://www.lacie.com (USB Drive, goes on key ring)

iPhone:http://www.apple.com/iphone (serves as phone and ipod)

watch

Well a man should only worry about three things, pounding beers, slaying bitches, and owning land so to answer that question....

-6 pack of the cheapest beer possible
-huge buck knife for shaving (even tho real men have bad ass beards
-pack of cigs
-keys to an awesome man cave
-flannel shirt
-levis
-a key ring that is unreasonably large
-a real leather wallet that is so large you sit slanted

really i can't think of anything else a man should have

This is entirely a matter of personal choice. If you're ok with carrying a manbag or a small backpack/messenger bag, you can carry more AND save yourself from wasting plastic bags and carrying purchases.
Feel free to pick and choose from this list.

- Wallet (I prefer the slimmy)
- Drivers License/State ID/Student ID etc.
- 3 Business Cards
- Debit and/or credit card
- Cash (I find that 20-40 is fine. Make sure to bring at least $1 worth of quarters just in case)
- Metrocard/faresaver (your equivalent)
- Lipbalm (IN A TUBE. I cannot stress this enough)
- Discount Card (Consolidate all of them using a service like Just One Club Card)
- Cell phone (having a smartphone negates the need for having an MP3 player as well)
- mp3/iPod
- pack of breath mints/gum
- pen (Use something classier than a bic. I recommend a Uniball Signo, TUL, or a Sharpie Pen)
- keys (attach a small USB drive loaded with the portableapps.com suite for good measure)

Depending on your situation:
- Cologne (bring either a sample spritz bottle from department stores, or make your own small bottle or roll on using bottles from dollar stores or Sephora)
- Moisturizer (from dry climates)
- oil blotting paper

gun. get anything else you need by wielding the piece. pays for itself.

mind-boggling how many men consider chapstick as a necessity. really?

wallet (with whatever fits in that)
pocket knife or multi-tool

anything else is an accessory

condom

On my keychain there's a swiss army knife with a pen, bottle opener, LED light, and screwdriver built in.

USB thumb Drive.

1. Chap Stick
2. Mint Gum
3. iPhone
4. Wallet*

*With one of these tucked inside

You are now ready for any situation.

How do you guys fit so much crap in your pockets?

Keys
Gum
Wallet
Cellphone
Chapstick

1. Wallet
1a. Cash (around 45 dollars, in various bills)
1b. Debit Card (one for my main bank, another emergency card that is just the money left in my first bank account)
1c. Drivers License, School ID
1d. condom (switch it out every month or so, body heat weakens the latex
2. Cell phone
3. Keys

OPTIONAL SECTION:
These vary depending on where you live, laws, and what you do for a living
1. knife
2. watch (the time is on your cell phone)
3. ipod (if you have a long commute)
4. pen (not a bic, bring one you could write on a napkin with)
5. multitool

Alright, wow some guys must be carrying man-purses around to fit that much stuff.

I agree with most though:

A fat wad of cash with varying denominations, i suggest carrying no less than 200, not everyplace takes credit cards, and sometimes you don't want a record of where you've been...

Credit card with no balance and high limits, when your lady friend needs to be impressed.

a pocketknife is a must, it just always comes in handy, i personally carry a switch blade, but due to varying state laws on their carry, it the choice is yours. Nothing too big just something to use in a last resort in a fight or to snip off some loose threads from ur shirt.

Chapstick? ok that is cool to keep in your car but honestly it is just a bit too bulgy for my pants.

Cell phone, obviously you need a cell phone

a pen would have come in handy many of times for me, but unless you are wearing a 3 piece just ask the bartender for a pen to get some digits. Don't pull out your cell phone to take a number unless it is an absolute last resort. Just plain tacky.

as for the concealed carry, well i never leave home with out my xd .45 in the small of my back or in my car depending on my destination.

a lighter is always useful regardless if you smoke or not, you may need to burn through ropes that are binding your wrists or light a cigarette for a lady who only smokes when she drinks. Don't ask about the ropes, it was a wild night.

I can think of some other things, but they are more for traveling over seas or in mexico, like a stainless steel wire sewn into the seam of your jeans, a hooked piece of wire or handcuff key attached to the back inside of your belt, and some other things that would aid in escape from drug lords or terrorists. This is the only time i would be country enough to keep a multi tool attached to my hip.

Cheers!

-your wits
-mints, not gum. Chewing can be innapropriate at times.
-a small blade that can be brandished quickly if needed
-handcuff key in sock or shoe
-an alibi

Necessities:
-Money
-Camera Phone
-Listerine Strips

A lot of people pretty much said this, but I think it's important to restate it. A man should carry only a few things and pick up what's needed along the way.

In wallet: Cash ($25-100), debit/credit card(s), ID

On person: mobile phone w/camera

and of course... keys for car/home.

Just say "no" to merses and manbags. Unless you're a student, lose the backpack. If you have a laptop bag then you're free to carry other things too.

One thing that came up in the answers that I hadn't considered but thought a worthy, if it's small, thing to carry is a pocket knife. A small flat one that fits in the wallet is a good idea.