I'll echo what has already been said ... pre-prepared foods by nature are high in sodium.
So that means any processed foods ... bags, boxes, bottles ... that require little or no work on your part!
Store bought dressings yes ... high.
It really does not take much work to make your own, and once you start doing that you will soon discover how tasty it is, even with the low sodium ... and before long, will not want the store bought.
That goes for a lot of foods.
Sodiums are a preservative, which is why many of our prepared foods have such a long shelf life. For example, a cup of corn flakes has more sodium than a cup of salted peanuts!
The other consideration in your cooking is to choose ingredients that will add flavour. Favourites of mine are herbs/spices, fresh garlic and onions.
Going low sodium does not mean you have to sacrifice taste.
Though when I have had low sodium prepared foods ... they sure have.
And it just convinces me all the more why I make more of my own foods!