Here are eight canned foods that can make a real difference when grocery shelves get unpredictable. Not because they are trendy, and not because anyone should panic, but because these are the kinds of items that quietly become harder to find when processing plants close, harvests come in smaller, import costs rise, or stores start cutting back on slower moving products. A lot of people only notice a shortage when the shelf is already empty, but by then the cheapest cans are usually gone first. S