Poison resistance is a lot easier to incorporate into everyday life than an elemental resistance. There are many things that we enjoy that are technically poisonous, such as anything alcoholic, and any vegetable in the nightshade family (tomatoes, potatoes, eggplant, peppers of all kinds), but most of them are either only poisonous in very large amounts, or are commonly cooked, which breaks down any harmful compounds and makes them safe to eat (some types of fungus can't be eaten raw). A person who is resistant to poison would be able to eat some foods that humans normally stay away from. The best example that comes to mind immediately is fly amanita mushrooms (the famous red capped white-spotted mushroom), which are both poisonous and edible with proper treatment. Dwarves might not need to boil them twice before cooking to break down the poisonous compound. They might also be able to consume green tomatoes in large amounts without fear.
Elemental resistances might appear in a more subtle way. A tiefling never has to wait for their lasagna to cool, never has to blow on their food, never has an incident of putting too-hot food in their mouth and then huffing to try and cool it. Maybe tiefling cuisine involves more flambe dishes, or dishes served while set on fire with spirits.
Someone resistant to cold might never suffer from brain freeze, a cold-headache related to eating frozen food, and their cuisine has a lot more cold dishes, or frozen foods.
Maybe acid resistance is not getting that stinging mouth sensation when eating food with a lot of citric acid, or not minding sour foods.
Yeah, that's about it, I can't think of anything food related for someone with lighting or thunder resistance.
