Potatoes
Potatoes go great with any kind of meat including tri-tip. You can bake or roast them and then mash them up or slice them into wedges for an easy side dish.
Rice
Rice goes well with almost any kind of meat but it especially pairs well with tri-tip. Try serving brown rice or long-grain white rice cooked up with butter, salt, and pepper for a delicious side dish that will go well with your meal.
Vegetables
Sautéed vegetables like broccoli, carrots, and cabbages go well with tri-tip as long as they are not overcooked. You can try serving steamed spinach or kale alongside your tri-tip roast for something different. Try also roasted vegetables.