The Swedish army issue survival knife by Frosts of Sweden. 4" stainless blade, molded-on plastic handle, ugly ambidextrous plastic sheath, practially weightless. Dirt cheap - carry two or three.
The Swedish army doesn't anticipate a lot of knife fighting, since it issues rifles, but it does expect soldiers to have to get through a few cold nights in the north woods. The Finnish army used knives of similar size, though more traditional materials, to good effect as tactical knives, back when they were fighting Russians.