Dunbar

FYI, they make two sizes of the Micro Caddy. The small is .23l and the medium is .4l. The small one is pretty darn tiny.

The main advantage of the Micro Caddy is it prevents rubbing on the inside of your shorts (if you have that problem in the first place.)

Campag4life

Since I started this thread way back when, just want to say the Lezyne micro caddy has been great...what I still use.
Holds enough emergency stuff...I don't access it on daily rides..jersey for keys, cell phone etc...but holds a tube...couple of inflators, tire levers, spare money, couple of allen wrenches and room for a little more stuff. Very compact and fits tightly under the saddle versus hanging down. About $20. Btw, I carry two inflators because if a slow leak I try to nurse it back to the car which sometimes takes an extra inflator. I hate changing tires on the road.

SpeshulEd 

This. Every saddle bag thread gets the Dual mentioned multiple times for good reason. It's the perfect saddle bag.

DXchulo

I have the Arundel Uno, which is a little smaller than the Dual. It fits a tube, 2 tire levers, and a tool. It just barely fits all of that, so it's perfect. It looks about as cool as a saddle bag can look, IMO. I just got it a few months ago, so I'm not sure how durable it is yet.

Before that I was using Pedro's Blowout in size micro. It kept falling apart on me, though, even after I sewed it back together a couple times.

Fiery

I've also recently bought an Arundel Uno. I've managed to fit a tube, two levers, a smallish multi tool (this one, minus the bag it comes with), a patch kit with a spare quick link (this one) and a spoke key (like this one). The bag is stuffed but holding. At some point I will replace the tool and spoke key with a more compact tool that includes a key to make it all bit more compact. I use a mini pump fitted to the frame, so no CO2 in the bag.

Johnny Rad

Sounds like the Uno is too much of a good thing ... prob won't fit 2 tubes, 2 CO2 cartridges and an air chuck.

I'll check out the Dual. I like the way it mounts further away from the post.

Dunbar

I have the medium Micro Caddy. It fits one tube, 2 CO2 cartridges, air chuck, tire lever, lightweight chain breaker and a small mult-tool. I carry a second tube in one of my jersey pockets. FYI, lightweight butyl tubes are more compact so they work better when space is limited.

Johnny Rad

I'm all for lightweight tubes, but prefer standard weight tubes in my saddle bag so I don't have to pay much attention fixing flats out on the road.
With folks waiting on the roadside with an unplanned delay, I appreciate the more forgiving standard tubes so I can slam them in and be done with it.

Shimano Pro Mini bag is intriguing now ... it's shape tapers towards the seatpost. Not sure the Arundel Dual or Topeak Mini Aero do the same...

bugly64

This is my second seat bag from EBay. The first one was not waterproof and is going on my wife's bike.

Fiery

No strap around the post is more important than bag width in my experience.