I don't carry nearly as much around with me as some others in this thread, but I do have a decent supply in the event that something goes wrong. I have an extra large carrying case with three larger batteries (900mAh, 1000mAh, and a 1300mAh), two cig-sized batteries, a very small packet containing some adapters, comfort tips, and a thumbtack (comes in handy for various things), four Vivi Novas, ten CE3's, and a charging cable/car charger. It's pretty much all the e-cig stuff that I own, except for ten or so bottles of juice that stay in my cupboard at home and a few more charging cables.
I used to have more, but gave quite a bit away to someone I met over the weekend. Being generous with my supplies is starting to get expensive, but a lot of people aren't comfortable with a "sales pitch," and are much more receptive to the idea of switching to e-cigs if they're given something to experiment with first. Besides, this lady has COPD and says she can't quit smoking. I really hope the stuff I gave her can improve her health.