I use vials and needles, both for the space and the cost. insulin in pens costs about 4 times as much as the same thing in vials. For those of us on fixed income, that can be a lot! Mine stays in the veggie bins at the bottom of the Norcold refrig. We have been out up to 4 months at a time, and I always try to carry extra in case we don't make it back when we plan. depending on you type and dosage, consider vials. one vial will last me about a week, one pen about three days. you can store at least two vials in the space of one pen. For me, injectins with a syringe is much easier than with a pen. Needles are the same size.