I agree a Bowline, 'Round turn and 2 half hitches' and a Rolling hitch are essential.
Knowing a variety of bends is very useful:
Double sheet bend
(very quick, reasonably strong, good for ropes of different diameter)
(very strong, use only if the ropes do not have to be untied)
Zepplin or Alpine Butterfly bends
(strong, knots can be untied). Although the Zeppelin is marginally better I prefer the Alpine as it is so easy and follows on from the Alpine loop.
(very strong, good for very thick line, needed for learning
the Diamond knot used for soft shackles)
Alpine Butterfly loop
(very useful as unlike the bowline, tension can be put between any component)
is handy in general.
Since using soft shackles for the snubber, I have not needed the previously often used Prusik loop & Klemheist.
Can't think of anything I use a clove hitch for, except it is a component of lots of other knots eg the handcuff