Thanks all-yes I suspect that your system does eventually get full and can take more more of some food/substance.
So I'm starting a five day stint(early). Apart from fruit, which is a no brainer, it is bloody hard to avoid bread/pasta etc. To further complicate things I can not keep things cool effectively. I discovered a John West Light Lunch. Its tuna based and come different styles. To be honest it does look a bit like cat food-but is not that bad, and does not need to be kept cool.
I know they are expensive but M&S do some really good ready meals. Check that they are not microwave only.
If anyone is willing lets try to develop a menu and try it out and post field reports.
So all agreed on fruit and nuts.......