If you need fuel, then Perranporth has a tarmac runway and last time I was there (a year or so ago) they were offering reduced or free landing for aircraft uplifting fuel on the way to or from the Scillies. Superb approach over the cliffs on one of the runways.
Scillies themselves are superb, but beware sudden fog blowing in from America!
There is a superbly-sited cafe 15 mins walk from the airfield which sells freshly-caught local fish overlooking a bay. From the grass parking behind the Tower, follow the foothpath downhill into the group of houses, turning left along the street. When you get to the beginning of the seafront, turn left up a lane and it's about 70m on the left. Unfortunately I can't remember its name. It makes a good place for lunch if you're only there for the day.