Generally, to
disassemble a piece of
equipment in the
field (
outdoors, in use, in transit, in
combat) for
repair, cleaning or
transport.
WRT cigarettes, it means to roll the butt between your fingers so the tobacco falls out and you're left only with the filter and what's left of the paper. Pocket that. Cigarette butts are not only unsightly in the outdoors, but they're toxic as hell and present a choking hazard to small animals. So don't be an oaf.