If you aren’t staying in St Ives it’s easier to get the train in the branch line runs between Penzance via Carbis Bay and St Erth.
You can get amazing food there. There’s one family that own most of the great restaurants and they are all fabulous. My order of preference:
Porthminster Beach Cafe
Porthminster Kitchen
Porthmeor Beach Cafe (especially breakfast, get there early to get a pod outside and book early to have dinner in a pod)!
The Loft is good.
Thai Tapas apparently great.
Kids love the Rum & Crab shack.
Best fish and chips anywhere (not just St Ives)- Balancing Eel just behind the Sloop In on the harbour.
It’s nice to walk from St Ives to Carbis Bay around the headland, easy 30 min stroll and the hotel is gorgeous, but I’d just go for coffee as it’s hideously expensive (£19 for spaghetti bolognese iirc 
).
A gorgeous walk, about 2,5hrs, across the fields and tracking the coastline, takes you to Zennor where there’s a v old pub called the Tinners, they do a great Sunday lunch or food generally, with a big beer garden. If you don’t want to walk back get a cab or check bus times, bus stop 2 mins away. If you want a more serious hike (4+ hrs) you can take the coastline route. Google St Ives to Zennor walks for guidance.
The Gurnards Head pub is renowned for its food if you fancy a change of scene.