I personally avoid the issue of breakdowns by always carrying with me:
20+ feet kanthal
Tools, both hex keys and multi-tool
3 - 4 batteries, charged
60ml juice
SS tank replacement (if the quartz cracks)
Spare o-rings
Spare spring, as well as magnets
4 - 6 extra wicks
Needle (sewing type, for poking holes in things, clearing clogged wicks, or bracing a wick for coil-wrapping)
Spare syringe and blunt needle - in addition to the Zeninjector that lives in my pocket
Flashlight
Business cards of suppliers for people who ask questions
...all in a "diabetes" zip-up bag that's about 8x2x3 in size. Lives in my car mostly; I pop it into a coat pocket or carry it if it's hot. No matter what happens to my Zen~, I can fix it in short order with this kit. I'm waiting to be able to get spare screws, however.
-Insp. 2211