Buy gluten free burger buns, bread, and wraps that do not contain any high FODMAP ingredients like inulin, apple or pear juice, apple fibre, concentrated fruit juices, honey, or high fructose corn syrup. Also check what low FODMAP flours have been used, avoid gluten free products that contain amaranth flour, lupin flour, chickpea/besan/gram/garbanzo bean flour, lentil flour or large amounts of soy flour or coconut flour.
Garlic infused oil is found in the oil section of your local supermarket. It should be clear with no floating bits of garlic. You can also make garlic infused oil at home by frying garlic cloves in cooking oil, until they are golden and fragrant (then remove the garlic before you continue cooking your meal). This is a low FODMAP way to capture the garlic flavour as the fructans can't leach into the oil.
Fresh lemongrass is found with the fresh herbs in the chilled section of the vegetable aisle. Avoid using lemongrass paste as it often contains lactose or onion/garlic powder.
Buy a bunch of green onions/scallions with long green tips. You can use the green tips of the green onions/scallions (which are low FODMAP) and not the white stem when cooking.
Check your dried chilli flakes do not contain onion or garlic powder.
The amount of wheat in regular soy sauce is low FODMAP, however if you are feeling concerned you can buy gluten free soy sauce (Tamari).