Agree on bowline, figure-8, clove hitch, rolling hitch, cleat hitch, two half-hitches/fisherman's bend.
I don't find the square knot useful--with modern synthetic lines, it slips under load. When made into a shoelace knot, with slippery ends, then it is useful for sail ties and less likely to slip, too. If I really want to tie two lines together so I trust them, it's two bowlines.
I almost never use the clove hitch either, the lead never seems right. those who find it useful, could you enlighten me?
The only time I use the clove hitch is when I center my tiller.
My essentials list:
1) Bowline - essential
2) two half hitches
3) sheet bend for joining two ropes - do not use a reef knot for this!
4) anchor bend