At Ông Lang, the village and its approach roads give the beach outing a second layer. You can make food part of the decision rather than an emergency after the sand: choose a simple meal before the beach, or leave time for dinner afterward. The restaurants are not all on the waterfront, so do not confuse “in Ông Lang” with a sea view. A village table may have better value for the meal you want, while a shore table pays back in atmosphere. Those are different reasons to choose a place.
At Vũng Bầu, it helps to pick the food-and-rest arrangement around the bay itself. You are going for a more focused visit, not for the density of alternatives found along a central street. Bring drinking water and do not build the plan around finding the same range of snacks at every approach. If you need a shower, changing place or a long shaded seat, settle that with the business you will actually use. A meal purchase and a day-use facility are not necessarily the same offer. For a group with different priorities, make the meal the shared part of the outing: some can walk, others sit with the view, then everyone eats together. That is more pleasant than moving the entire group every time one person wants a drink.