[chooseaname]

Two knots: bowline and trucker’s hitch. You’ll need them one day.

[JshWright]

Trucker's hitch isn't really a specific knot. It's a technique that can use any number of knots (you just need to be able to put a loop in the middle of the rope and tie some sort of securing knot in the running end).

[cosmincimpoi]

Also Zeppelin and constrictor for joining ropes and tying bags.