The E-tool
Well if it were me I would love to have an E-tool by my side anytime of the day. I had a lot of encounters with huge tree stumps and lots of sand when we were told to "dig in". The only reason why I favor the E-tool it's because I know how to use it, I am comfortable using it, especially in close combat, then again if it the enemy ever got that close to me, I should give up on owning rifles/pistols. Of course if someone with a katana, machete or any other long knife comes at me I would want to have my Beretta PX4 Storm .40 with 14 +1 rounds. If you've never seen an E-tool click below
You can also use the open end of a canteen cup, just grab it from the bottom and bash his/her face in.