I've always used Carradice saddlebags on my bikes - I prefer the Pendle because it's big enough for all my stuff (Road Morph, patch kit, spare tube(s), levers, multi-tool, leatherman, first-aid kit, lock, rag, saddle cover, spare batteries, roll of duct tape, wallet, cell phone, smokes, headlight, clif bars) plus still has room for my lunch and a jacket. Yeah, I carry a lot of stuff for commuting and long distance rides, I like to be prepared.
Now, after many years, I have a road bike again - no fenders, no rack, nice and light - a sport/recreation bike, not a workhorse like my other bikes. I really don't want to slap the Pendle and it's SQR rack on it - it's probably overkill for what I 'need' to carry, it doesn't really look good on a road bike, and it does tend to flop around some when climbing. So I've been trying literally dozens of seat bags to try to find one that would fit essentials, plus still have room for a jacket and other 'just in case' things, yet be light, decent looking and secure.
Until now, every seat bag has been too small, about 240 cubic inches tops (more like 120 in reality), with the exception of the Carradice & Rivendell bags, which are too big, heavy and bulky for a road bike. I got to thinking about a small rack trunk bag on one of those seatpost-mounted racks...but again, too darn big, ugly and heavy. Then I saw the Nashbar Pack/Rack system and was thinking about trying it...until I stumbled upon a better version of the same system - the Moots Tailgater.
The small rack attaches to the seatpost and is made of titanium - light as a feather. It has two bags, one on the top, one on the bottom, each with about 250 cu in capacity. The top bag has a bungee type tie down and stuff sack. I am able to fit my essentials into the top bag, and stash a jacket, kneewarmers, etc, into the bottom bag. If I the jacket is wet, I can lash it to the top of the top bag. Loaded, it weighs about half of what my Pendle and SQR weigh empty - and it doesn't flop around.
I think I have found close to the perfect bag for those of us who want to do long day tours on a fast, light road bike - bigger than most under-seat bags (about 500 cu in) - smaller, lighter and more secure than Carradice bags - the only thing missing is a way to attach a rear blinkie...but I see some ways I can rig one.
Edit: the Nashbar version is a whole lot cheaper, but doesn't seem to have as much capacity, no top bungee/stuff sack and the weight/material of the rack itself is unknown, but I'll include the link for those that don't like the $139 pricetag of the Moots, but want to try something similar.
And no, I don't have any connection to or interest in Moots whatsoever.