I went from Marathon Racers to Schwalbe Kojaks and picked up a lot of speed and reduced rolling resistance. The Kojaks are recommend for street\pavement use only.

I like narrow handlebars - they fit me better and reduce wind resistance. So I grabbed a hacksaw and sliced off liberal amounts of handlebars on either side. Last week I fitted BBB Ergo Sticks (kinda like Cane Creek Ergo Bar Ends) and now feel like I have the perfect combination for my vehicle. Multiple hand positions, enough to go down low, enough to climb and able to achieve a tuck position with any hand position. If you find a discarded drop bar, you can chop that to make a bullhorn bar which also works well.

I converted my Dahon Helios to a 66 gear inch single speed after having experimented with 62 and 72 gear inches. As I ride several bicycles, I use a cheap helmet mirror so I have one practiced move for checking traffic behind me regardless of which bicycle I am on. I also mounted a large multiple LED light which has flash modes and a flashing red Planet Bike Blinky on my helmet so I have the same setup from bike to bike.

I use a standard rear bike rack on the Dahon mated to an expandable trunk bag. This preserves the narrow profile of the bike for city riding and does not pose additional wind drag on the bike since the bag is directly behind me. Some Dahon rear racks are so low they are unusable for side panniers due to heel strike issues and road clearance.