Remember the wedgies you used to get during gym class? This is different, so quit your whining. Straight outta Novara, REI's house brand for biking, the Expanding Wedge is a perfect little seat bag that mounts on your seat post, with one important caveat, so read to the end for once in your ADHD-driven existence.
The Wedge has a main compartment with a side zipper and key tether that's big enough to hold a 6' cable lock, multitool, spare tube and some smaller odds and ends in a separate mesh section. When I get ready to head out I'll unzip the expanding part and throw in a cell phone, energy bar and garage remote or keys. The Wedge attaches easily to your seat rails and quickly untwists so you can take it with you when you lock your bike up at the pub. There's a velcro tab to keep it fixed to the seat post, and the webbing strap on the bottom is perfect for keeping your rear fender on the straight and narrow, or strapping on a pump. We've heard mention of people using extra clips so they can switch the wedge between bikes, but we can't find these mythical extra clips anywhere. Anyone?
There's even a place to clip an LED please-don't-hit-me light or reflector on the back. OK, so the caveat is this: small bikes, specifically those of the SheFlogger category, may not have enough seat post showing to fit this bag. We'll keep searching for an alternative, but for bigger bikes this is the bag to beat. If you're in to beating bags, that is. And why shouldn't you be?