I LOVE my Brompton, and have spent much time researching accessories for it. Here are the accoutraments I’ve bought for my Brompton, and hopefully it’ll save other Brompton owners time, and/or make them aware of accessories they don’t known about.
EZ Wheels: The stock wheels that let you roll the Brompton while folded suck. The EZ wheels, let the bike roll effortlessly.
Replacement Grips: The Brompton grips are terrible. It took me a few months to replace them with the Ergon GP-2 and the only thing I can say is I should have done it sooner. Without a rack, you can’t go bigger then the GP-2s without affecting the fold. But, with a rack, I’m told you can get the GP-3’s, but I haven’t tried them.
Front Bag: This makes the bike so much more useful. I went with the C bag and I recommend it highly. While riding the Brompton, the bag is incredible - It’s waterproof, can carry a lot of stuff, has a waterbottle/coffee tumbler holder, and has deep pockets I can trivially access while riding. Off the bike the bag, the bag is quite comfortable with a nice shoulder strap, and really wide throat which makes it easy to pack and allows a lot of storage. Most surprisingly is how well the bag works when the bike is folded. You can fold the bike without removing the bag, and when folded the handle on the bag can be used to pull your bike along. Also, with the bag (and the rack) you can go into shopping cart mode. Shopping cart mode lets you use your Brompton like a shopping cart, which makes it much more welcome in stores.
Rack: As a rack, I’d never use the rack because I have the front luggage, and because I’d have to remove the contents of the rack to fold the Brompton. However by having a rack, I can put 4 EZ wheels on my Brompton, which lets me roll the Brompton while it’s folded effortlessly. This is incredibly useful as it removes much of the need to carry the Brompton while it’s folded. The rack also allows men to use the Brompton in shopping cart mode. Because I didn’t start by buying the Brompton R model (the model with a rack - which I highly recommend), I bought the after market Nitto rack.
Lock: The Bordo 75cm folding lock, is secure and will fit on the Brompton seat stay, even while the Brompton is folded. The lock looks like it was custom built for the seat stay. It’s very important to get the 75cm Bordo, as the larger Bordos will not fit.
Child Seat: I’ve got a 2 year old, and want her to come on my bike. I use the Tyke Toter , which I can add and remove from the Brompton in about 30s.
Touch up paint: The Brompton gets a lot of nicks and scratches, get some touch up paint.
If you have other acessories I should add to the list, leave a comment.