Here's a video on the Burley Travoy trailer. I use two large market bags instead of the smaller top bag. The Brompton takes the compactness of everything a big step forward to a new level. Right now, I've been walking up a fourteen foot ladder onto the boat with the bike, then I take everything down the companionway
in just a couple of trips.
I can honestly say, if you live within two miles of a grocery store, this method is much quicker than taking a car to do the same job. No loading groceries into the car etc.