The following would take at least a week to do properly
A39 from M5 via Minehead is a nice drive for a solo car.
We stayed two years running at North Morte Farm, lovely site, good views, small shop, near to two pubs, some electric points and I could get digital TV as well.
Woolacombe is a good place, expensive to park though, Red Barn does good food.
If you do this leave M5 and take A39 via Wachet, Minehead, Porlock, Lynton,, A399 to Ilfracombe, from there Woolacombe is nice (go via Morthoe), Croyde Bay is OK, Saunton Sands scenic.
Plenty of nice pubs, plenty of places to visit, two preserved railways, one is long and by seaside, one is very significant historically.
Barnstable is a good shopping town, then A39 towards Cornwall.
Bideford is OK, Atlantic Village shopping thingy, Appledore is OK but quiet and difficult to park. Westward Ho! is very seaside, with big beach and arcades.
Haven't done Clovelly yet
In Cornwall Bude is interesting, I need a visit, so far just passed through. Also has Cornwals only canal!
Wideouth bay - been past - looks nice on internet and maps.
After this Boscastle and Tintagal, Port Isaac, Polzeath, Rock then back to A39 and Wadebridge - which is an OK little town.
Padstow is nice and well worth a half day visit.
The B3276 passes some lovely beaches on the way to Newquay, beautiful scenary.
Newquay is good for drinking and for the beaches
Near A3075 now and lots of touristy things to do including a dairy farm and a longish narrow gauge railway.
If you rejoin A39 here it goes via Truro to Falmouth
The B3275 takes you past Perranporth (Seaside Rescue), St Agnes (nice place with pubs), Porthtowan and Portreath are OK for an hour or so to say you visited, there is a Cornish Goldmine place with a Delorean, just up from an LPG installer!!!! Redruth, Carnbrea are OK
St. Ives is lovely except for the seagulls and driving on the harbour front.
I'll leave off here - next bit Lands End peninsula