I have a Valco Universal cup holder. I bought it off Amazon for like $15. I haven't put it on yet, but it came highly recommended by a bunch of woman from my local board.
I got a Universal cup holder at a baby store where I bought the stroller, and I have to say, it pretty much sucks. The City Mini has a pretty thick handle bar and it just didn't fit, so I stuck it on the center pole but had to remove the plastic inner clamps to get it to fit. So its on there, but not securely and it rotates. Basically, I can get one cup or water bottle in there, but not securely. It only stays upright by dint of its own gravity.
Re: Did you add cupholders to your City Mini Double?
Baby #3 due September 12, 2014!
cupholder for you or the kids?
for the kids--not yet
for me--day 1! The bought the Sunshine Kids Parent Console from Amazon for $10 and it works great!