apartment therapy changing the world, one room at a time

I have a question...
It's not design related, but I feel comfortable here and I know you folks have great answers!

We are going to NYC next week with our 4 year old. We will be using public transportation to get around... so my question is: Do we need to bring his booster seat for cab rides and such or do people generally not worry about that? I can NOT imagine carrying that thing around and I probably won't.. but I'm just curious about how people deal with that.

THANKS!!!
Melissa