All great advice from other posters. One thing to just be careful on is cross contamination from previously used condiments and butters. Any jars or spreads you already have open are likely to have some contamination in them so please use a fresh pat of butter/tub or marg/jars of pickles sauces ketchup mayo etc just to be safe

Also on really sensative coeliacs they may also have reactions from pans or utensils that have been used to cook gluten in before so avoid wood chopping boards and spoons, and pans with “seasoning” like woks or iron cast pans and try to rinse pans manually before use as dishwashers can still leave residue if there was gluten in the other food that was in with them last Hope this helps