Brompton Carrying Frame S-Type
The carrying frame (QFCFP-S) is part of the Brompton "S" front bag and can be removed by opening the Velcro tabs on the bottom of the bag. If you don't have use for a bag at all than this is the way to go. Carrying frames also have the advantage of very little wind resistance. Carrying frames come in standard and small sizes, make sure to get only the small if you are riding an S-Brompton.
Be sure to order the carrying block below if you don't have one your bike yet.