Cross contamination in jams, butter, margarine, peanut butter etc. It's easy to leave a breadcrumb in the jar from a dirty knife. Either have separate containers with one labelled clearly 'wheat free' or use spoons in your pots and containers. Lots of spices and seasonings have wheat in them. Only have wheat free versions in the house, that way mistakes can't happen.
Many people use the same chopping board for vegetables and bread.
And always a separate board for meat and fish. Make sure the board is scrubbed thoroughly after it has been used for bread or wheat containing products. Better still get a completely separate board. Ordinary pizza and wheat free pizza at the same meal. Separate the pizzas with another oven shelf between and a baking tray on it to ensure that the ordinary pizza does not drip onto the wheat free pizza.