Low-salt Cooking on a Barbecue
If you make your own burgers you don't need to include any salt at all. You could make them unseasoned but you may find you enjoy them more if they've got herbs/spices in them. This also holds for sausages if you can be bothered to make them. Marinades don't need any salt either, though of course you may choose to add a little. Spring (salad) onion and garlic are very useful if you're reducing the salt. 

Grilled veg is often best simply brushed with oil. I like to use chilli oil or pizza oil (chilli and herb). Along with steaks, chicken etc. you can also brush with a little oil and rub in spices or herbs. 

Many sauces you might add after cooking also contain a fair bit of salt. Making your own or choosing ones that taste less salty will also help. Ketchup, for example, varies a lot in salt content.

You're probably used to fairly salty food, but your tastes can adjust fairly quickly.