2_i 

For about a week now I am riding a Brompton with Vincita Nash rack bag. My interest in the bag was spurred by the need to off-load somehow my T-bag at times when I needed to carry my bulky laptop. Vincita advertised the bag as fitting and easily mounted on the Brompton rack. Finally the bag incorporates panniers that offer additional option for absorbing overflow.

The bag uses Rixen and Kaul (KlickFix) UniKlip mounting system that allows to mount and dismount the bag in a blink of an eye and keep the bag firmly on the rack, The volume, partially limited by a padding insert, of the order of 11 liter, is modest, just a third of the volume of a T-bag. However, it is fine for my purposes. The shape does not allow to place my laptop bag there, but I can put the latter into the T-bag and off-load bike related items into the Nash bag. As I park the bike at work in a secured space, I currently just leave the Nash bag on the bike permanently. It looks like it can fit nicely into the space under an airline seat so this may be its fate if I take the bike along in travel.

The bag comes with a rain cover. One of the photos below shows the content that largely fills up the bag. I can still squeeze a folding helmet in addition, before going for the panniers.

Overall I am happy with the purchase. The bag arrived from Thailand within 3 days without any elevated shipping price. Alternatives to this bag include Brompton Rear Rack Bag, that seems to be getting phased out but is still available from dealers, and a couple of rack bags from Rixen and Kaul that utilize the same UniKlip system.

Jipe

Ortlieb has similar bags with also a quick release system called Rack-Lock System :Ortlieb Trunk Bag RC and Trunk Bag these bags are 100% waterproof.

2_i 

Thanks, these could be indeed alternatives to consider. They grab the rack a tad differently and I am not quite sure that this will work with the standard Brompton rack, but should with different alternative racks. The Ortlieb cloth seems thinner. Vincita cloth is a relatively dense cordura seemingly akin to the Brompton rear rack bag and the Klickfix bags. The zippers in Vincita could have been thicker - they are thinner than in either the laptop bag or coat that I carry concurrently.

Schwinnsta

2_i, what kickstand? thanks.

2_i 

It is my current Top of the List ergotec/Humpert Liliput touted for a long time on the francophone Brompton forum. You need to use vise and mallet to reshape its mount a bit, making it grab better the nonstandard Brompton chainstay, but it is not a big deal. It has adjustable length and holds steady.