Thinking in real terms- you dont have access to german, russian, and american weapons in the even of an invasion.
Id hold up in a liquor store and make molotov cocktails.
Long range:
Cocktails (the real ones with oil, gas , and rubber)
Close Range
Clear Police Shield and fire axe (28 days later style)





Failing that, they're's always the evil dead way- chainsaw, axe, shotgun. But Personally I think a Katana for short range, (off with the head) aa .357 magnum or a desert eagle, and for long range, say go with a colt M-16. Or HK MP5. 12 gauge shotgun perhaps as well, any shotgun is good, it doesn't matter as long as you know how to use it, it's size and power fits you, and the shells are easy to obtain. 