Firstly, try not to look at it as "what you can't eat", rather a change in diet. Eating gluten-free doesn't mean you need to give up great foods. In fact, there's so many alternatives to gluten products (that you might not know about) that are just as great, or better! But don't be fooled, gluten-free doesn't necessarily equate to healthy, and many of the packaged foods contain more sugar, fat and gluten-free flours to make up for the flavour and texture.
As a general rule of thumb stay away from flour, bread, pastry, cakes, pasta, pizza bases, biscuits, most cereals or processed foods, such as sausages, soups and condiments, unless it clearly says gluten-free. Though it's always best to double check the ingredients to be sure.
Most supermarkets will have a gluten-free aisle, which will make it easier for you to shop products like baked goods, flours, breads and pasta — see, there's always alternatives.