Technology is increasing at an alarming rate, withe the discovery of the higgs boson, and the pictures taken by the HUBBLE telescope. How long will it be before we encounter more intelligent life? And what will happen when we encounter the intelligent life? We dont know how they will respond to us, nor do they know how we will respond to them. Thus, as a basic precautionary measure, it could only be intelligent to arm the masses so that they can defend themselves in case of emergency. The simplest of weapons is the crowbar, but it could have a number of different uses in alien invasion survival, including, but not limited too:
Using as a weapon against alien footsoldiers
Opening cans
Prying open manholes
And more!
As you can see, the crowbar would be an invaluable tool against aliens