Owen Hayward has developed the obvious roadside block by the side of Llyn Gwynant boulder (i.e. the next one down from the Gwynant Crack boulder and directly opposite the Elephantitus cave). The walk-in from the layby, through the gap in the wall and over the small stile, takes all of 30 seconds.
The best of the bunch is Roadkill 7A+, which tackles the rather fine undercut arete from a sds. Start with the lower of two diagonal edges for your right hand and fat pinch for your left. Clamp powerfully up the arete to jugs and a high but easy finish. A tricky number!
Next best is Roadbloc 7A, which climbs wall 1m left of Roadkill from a sds (if you're tall) /crouch (if you're shorter). Good powerful climbing starting with your right hand on the obvious pinchy finger jug on the lip and your left on a choice of sidepulls under the lip; then moving up past three sharp dink/pockets to get better holds and the big flake up left. Highball finish straight up the slab above.
At a more approachable grade is Gawping Grockles 6B+, which climbs the shallow groove feature just right of Roadkill from a stand start. Use jugs (right) and very sharp sidepull (left) to get the good sidepull in groove above (forming the left side of the block). Now span up left to jugs on Roadkill and finish up this (safer) or straight up.
The high wall to the right of Gawping Grockles can be climbed anywhere at grade 4 or 5 and gives good, if slightly scary, warm up probs.