A few hints on burgers & sandwiches for the sodium conscious:
If you like cheese, ask for Swiss- at 15mg/serving, its about the lowest sodium content of almost any cheese. Barring that, ask for cheddar, at 170mg or so. American- typical for most burgers- can be over 400mg per serving.
Many burger places actually season their patties. Ask if they do, then ask if you can get it without the seasoning. I've generally had good luck at Whataburger and TGI Fridays.
Ask for a different bread. Burger buns tend to be higher in sodium content, usually because of preservatives. Breads like sourdough, rye and others not only have lower sodium content, but may also improve the flavor of the burger...and are generally fresher besides.
Drop saltier toppings like pickles (substitute dry dill instead) and olives. Choose red wine vinegar instead of red wine vinegarette. Yellow and brown mustards are generally not bad, but fancier ones may be problematic. Tomatoes are great, but katsup is horribly salty.
I've found that using a salt-free butter on sandwiches I make at home is just fine as a spread, especially coupled with one of the various salt-free seasoning mixes. Things like Mrs. Dash Mesquite or Grilling mix is good on chicken or turkey. The steak mix is cool on Roast Beef or burgers.