Ages, assuming we had water and a heat source. I have jars of all sorts of dried pulses, rice, pasta, nuts and dried fruit, plus a spice cupboard, so we could live on daal, bean casseroles and soup. There are tins of tomatoes and more pulses, as well as flour, custard powder and various vinegars and other flavourings, so I could improvise a pudding most days, if we fancied it. The freezer is full of leftovers and veg, plus meat and veggie sausages and Quorn mince, so I could spin that out for a while, too.
We would get bored, and having no bread, milk or eggs would be limiting, but we would survive for a long time if we had to.