Is this something you need to do once or twice, or repeat multiple times per day? Dremels are quite multipurpose, but not if you need to make 10+ cuts per day.
Big full size bolt cutters would do it and quick, but probably won't fit n you backpack. Depending on clearance, an m12 portaband will easily and quickly do it; how big is your backpack. One battery could probably get you about 20 cuts, if that isn't enough, a 2nd battery is small enough to carry.
A cordless die grinder, many tools could work depending on how many cuts you need to make, what kind of clearance you have, how big and still fit in your BP, and price is always a factor.