There are so many things I'd qualify as necessary, but let me mention my short list first, and over time I'll add more.

Duct Tape, WD-40, Shovel ( a couple of different kinds), Machete, Wood splitting maul, axe (single bit unless you are a pro), a couple of different types of hand saws, hammer, sledge (persuader), screw driver set, pliers set, and a good variety of metric and english wrenches and sockets.