I have language students too and I think what Eric is providing sounds fine and is well within the guidelines that the schools give you which is: sandwich, crisps, fruit, cake/biscuit, drink. If they want more crisps they should buy them themselves. FWIW I take a packed lunch to work with me every day and only eat a sandwich and a banana and I'm a strapping great woman!
Most of the language students I have eat virtually nothing but crisps and chocolate. The bins in their bedroom are full of wrappers from junk food and empty coke cans. As mummylin says it's bloody annoying when they then 'aren't hungry' at dinner time when you've shopped and cooked a lovely big home-made meal.
For those who are saying 'well in Italy they probably have this or that...' in my experience all the teenagers - with the possible exception of the Far East and Middle East - want to eat Macdonalds at every opportunity. I usually ask my students if there's anything they particularly don't like, or would prefer not to eat, and often get a 'list'. My last Italians (two 14 yo girls) wouldn't eat cheese, vegetables of any kind, eggs, fish, or any kind of fruit. It makes cooking a meal very difficult. When I asked what they WOULD like to eat they said steak and potato or steak and pasta.
When I asked my Japanese student what she would typically eat for breakfast and dinner in Japan she said cornflakes and pizza. The last Spanish student I had (12 yo) said 'I don't like that' before dinner had even hit the table - every night for four weeks. The list of food she wouldn't eat was endless and included all vegetables and any kind of cheese. She asked for Nutella sandwiches for lunch because she didn't like any other sandwich filling, drank a massive bowl of chocolate milk for breakfast (refused toast, cereal, etc.) and had the usual binful of choccie wrappers on departure. My current Russian student is a blessed relief after that...
Stick to your guns Eric!
I do think we should try to accommodate language students up to a point as they are, after all, paying guests. However, we are not hotels and I don't think the whole household should revolve around them and their preferences. As someone else said, when you add up the cost of food, hot water, phone chargers/laptops left on day and night etc., the rewards are small, and it isn't feasible to provide them each with a tenner's worth of food every day (I'm thinking of my steak and potato girls here...:))