The Mini is the one. The Castelli Undersaddle Mini is just the one, the one bag to rule them all. Super compact this fit and forget under saddle, seat-pack can be crammed with a couple of (road) inner tubes a multi-tool, a spare link and a few $10.00 notes. Everything you could possible require on a ride. The strap uses a magic molded hook and loop fastener that can be trimmed at home and that wont fur your shorts.
This Mini bag is also weather resistant as is the zip. (OK its not totally waterproof but its better than most) the zip sits in a little cave so it stays silent and doesn't open mid ride. The rear wordmark is reflective and the lining is in a pimp corporate red. Could you ask for more? With the Castelli Undersaddle Mini its going to be a long love affair.
Water and stain resistant materials
Water resistant zipper
Water resistant construction
Adjustable hook and loop attachment strap
Internal storage pocket
External dimensions 5 x 5 x 13cm