I believe in full SHTF scenario ammo would be one the best currencies. also stuff like cold medication, painkillers, antibiotics, soap, bleach, salt (deep inland), fire-starting tools/supplies, hand-tools.
silver will have it's place but much later into SHTF, when first town-ships and organized trade re-establishes. Untill then people will have easier time using natural trade than currency.
although SHTF scenarios can vary significantly. Not every SHTF will be full-on TEOTWAWKI. SHTF can be small, short term, localized to certain degree. it might be that government institutions will not completely fail. Maybe some local states, counties, communities or mil bases will be able to stay in control and expand control of certain areas or aspects of life in near vicinity. variables are almost infinite and will affect final outcome of the scenario. can't predict every aspect 100%.