Depends.

Road/racey bike: Sew-up, frame pump, and a park MT-1
Commute/most bombing about applications: Tube, patchkit, pump, multi-tool
Back-country riding: Same as above, but add a spare cable and shock pump if applicable, multi-tool is upsized to include one with a chain-breaker
Loaded-touring: Add a second tube, spare spokes, spare tire, some ball bearings, enough tools to remove cassette, BB, headset and cones, grease, oil, etc, bits of chain and misc small hardware.

Most of my rides are 50 miles or fewer. Some are club rides and some are solo rides. Here is what I usually carry.

Spare tube
Tire levers
CO2 inflater and a couple cartridges
Allen wrenches to adjust saddle/seat post
$5-10 cash
Cellphone
Photocopy of my driver's license.

I carry the usual miscellaneous tools, some CO2 cartridges, a spare tube and some of those Park emergency tire repair patches and most importantly one of those little pairs of glasses in the plastic tube so I can see well enough to actually make a repair.

4 Oxycontin and a flask of bourbon.

I take it you have been going for rides with BG.

I have taken to carrying Drambuie in my flask and quite often mix up Celtic Crosses (Jamesons and Drambuie).

Irish Mist is my poison of choice...

Aaron

Cable
Kevlar Spoke
tire levers
small zip ties
small park chain tool
patches and glue
3' by 3' square of tyveck to sit on(chiggers, tics, mud, stickers and roadkill gasket)
Park multi tool, it has to much for any one bike, but it seems to have enough for all of them and thats better than picking out individual tools for any one bike
small multi tool with cable cutter
spare link
Up to three tubes
tire boot made from tire with the bead cut off
cell phone, credit card, cash and ID

When touring I might take more.

if there is no pump on the bike, either a Superflate with three co2s, or a short Avenier pump that fits in my seat bag and has both prest and schrader.

Yesterday I did fifty miles in the heat, and at the last minute threw a canvas sun hat in my jersey pocket. Really glad I did as it was a three flat day, with only two tubes, so twice I had to sit in the direct sun, at 104 degrees. One self tapping sheet metal screw, a steeple nail, and some mystery object that I never found.

Usualy take three tubes and a patch kit, but have had a run of luck with not many flats.

who needs tools?

oh wait ...those are tools.

That's about what I do. I usually also have a spoke wrench on my key ring, and, depending on the bike, I might have this multi-wrench.

Patch kit
Tire levers x2
Spare tube
Allen keys to fit the fasteners on my bike
Teeny adjustable wrench for the few hex bolt heads on my bike (will replace those with Allen heads, and dump the wrench)
Chain tool with the handle cut short
Dinky little ratcheting screwdriver that has Phillips on one side, flathead on the other (will replace this with a smaller screwdriver, since all it will ever be used for is limit screws on derailleurs)
Spoke wrench

On a long ride, add

Shift and brake cables
Another tube
Extra clipless pedals (the kind I use are very small/light, and a clipless pedal goes wrong on a ride, you are comprehensively screwed: low odds of finding a replacement at some small town sporting goods store).
Allen key for the pedals

I like the duct tape idea for sidewalls.

I use a canvas Mopha tool roll on my vintage bikes. It tucks in nicely under the seat with a toe-clip strap. Inside it holds a tube, patch kit, duct tape, tire inflator, 2 tire levers, 2 x CO2 cartridges, Park multi tool, 4 piece wrench set 8-11 mm (Craftsman mini ignition wrenches), spare chain link, 1 ea. brake and shift cable and half a dozen zip ties. There is room for more stuff if you want and it looks much better than a seat bag on a vintage ride.

On my Kestrel: nothing.
No wedge bag becaue of the aero seat post.
Tubular clinchers. Cell, ID and $5 in the jersey pocket.

On my Cinelli: wedge bag, small Zefal.
Cell, ID and $5 in the jersey pocket.
1 tube, 1 CO2 w/inflator nozzle. 1 lever.
2 allen wrenches for saddle/stem/cables.

Long rides, Cinelli only: wedge bag, small Zefal.
Cell, ID and $5 in the jersey pocket, 2-3 snack bars.
2 tubes, 2 CO2's, inflator nozzle. 1 lever.
2 allen wrenches, Park mini-brute chain tool.

for my next long ride, I'm putting stuff in the SAG vehicle, feeling good about it.

Spare tube, Mafac toolkit- with a screwdriver and a couple of Allen keys and a chain tool added. Fits in a pocket easily.

The list is different for each bike. Minimum elements are
Patch kit
Spare tube
Tire irons
Frame pump
Cell phone
Wallet
Home keys

On the tandem I carry a spoke wrench and small screwdriver.

Food, snacks. If you can have a picnic or at least a snacnic, the ride isn't worth doing.

Chain tool? Hmmm, a few years ago my chain jumped off the RD and got caught under the rear wheel so I skidded on it for 10ft or so. It didn't break.

Now why didn't I think of that?

By the way, I insist that my tire levers be steel. I have to shop around to find them. Alu and plastic levers seem just stupid to me.

I carry my wallet with me 7 days a week, no matter where I go. It has my credit cards and ID, etc.

Not only am I a minimalist, I'm also one of those saps that always thinks everything really is going to be alright

Contents: spare tube, a couple allen keys for cleat adjustment, a piece of Whidbey Island driftwood for clearing cleat slots, 53 cents and a small pocket brush.

Never underestimate the importance of proper grooming standards (just ask my Sacha)



I sometimes carry a credit card in there, and on rare occasions I have a cell phone in my jersey pocket.

DD

Snap-on 6" adjustable wrench; tiny Topeak allen key set; New Tinker Swiss Army knife; spare tubular or tube & tire levers. If the bike has no frame pump I take a mini pump & presta adapter.
The adjustable is useful as a spoke wrench, straightening tool (I recently used it on a chain that got caught & twisted) and light hammer. The S.A. knife has a scissor, tweezer, several screwdrivers and an awl, along with a couple of knife blades. I use one many times a day at work for dozens of tasks.
Like several other respondents, I use tools on other people's bikes more often than my own.

BTW, Tom of the Massive Thighs broke (and repaired) the tandem chain at least twice on the same ride. He's my hero.

Photogravity told me about that - impressive on both accounts

DD

To build on your list...

• tire levers (free from REI)
• patch kit (free w/ my saddle bag)
• allen keys (only the sizes I need)
• spoke wrench
• spare tube
• length of duct tape
• bottle of oil (free w/ my saddle bag)
• screwdriver (stubby Philips-head)
• pump (frame pump when alone, stand pump when hauling trailer)
• 6" adjustable wrench
• 15 & 16 mm cone wrenches by Park (when on the old Schwinns)

Some excellent suggestions.

I also carry a quick clot dressing. I have had to use two of them over the last 5 years (one on myself, one on another rider). They stop bleeding fast on deep cuts that would otherwise require constant pressure. They can tide you over until your spouse, an ambulance, or a generous passer by (thankfully with no regard for their interior) takes you to the ER.

I also carry two good old fashioned band aids. Ironically, I use those most often when repairing my bike with my tool kit.

heres mine 1. small crescent 2. hammer 3. pump & patch kit.............thats it.

Hammer?

I hate these threads. I always think I am carrying too much then find out something else I need to add. A chain tool and master link is a good idea even though I have never broken a chain.