I've lived in the centre of Penzance for over thirty years. Any journey by train to London takes many hours because reaching Exeter takes so long. Therefore a high proportion of Penzance to Paddington passengers during the week take trains that leave before the vast majority of shops, cafes, etc have opened. There was always a buffet on the station that did open early to the extent of a window through which hot and cold drinks and food were dispensed, plus sale of newspapers etc. This was only closed because it was forced out by whoever runs the station, can't remember whether that's GWR or NR, it matters not for the purposes of my argument. This was four or five years ago from memory: a friend of mine who was the main staff member had to go and work for the wretched Poundland. Yes, there is a catering van outside the station now (don't know its opening hours) but it certainly wasn't there for a long while after the buffet closed.
My experience of taking an early (7 a.m.ish) train from PZ was that, even with a buffet supposedly on board, it wasn't opened until after Plymouth i.e. the catering crew joined there, so it was upwards of two hours from leaving that you could actually get a hot drink: therefore the knowledgeable wanting a hot drink bought it at the buffet bar on the station before entraining. I would usually go to the buffet once or twice when making a journey in this direction, quite often purchasing hot food after three or four hours, say. On the way back, out of boredom as much as anything I'd probably go to the buffet at least twice. I really can't be bothered to stock up on drink before I get on a train, except a bottle of water: food is another matter, but I wouldn't bring hot food on board, an anti-social practice apart from any other consideration.
I gave up taking the train to London after a few years, for two main reasons:
1) The train fare, given I couldn't book more than a few days in advance, was as much if not more than the price of petrol for my car, even if I was travelling alone: if travelling with A.N. Other, it made no economic sense.
2) I was probably unfortunate, but my return journeys from London were dogged by delays and cancellations, often for bizarre reasons.
So my car took the strain, meaning I could travel when I liked and stop off if I wanted, or divert. There were some bad journeys, mainly at the London end, but on the whole I thought I was getting a better deal by car.
Now I'm in the position where my health and the increased unreliability of my car, which I can't afford to replace, make that means of travel near impossible. Train travel beckons again, and I've responded, once so far, my journeys being by HST. I don't look forward to the new trains for such a journey, having been on one for the minor Penzance to Truro section and finding the seat uncomfortable, despite not being surrounded by other passengers. If I'm to be denied refreshment for several hours too, and the opportunity to stretch my legs which is necessary for me, then I would seriously think very hard before deciding to make the journey.