Use ripe avocado instead of mayo when you make your egg or tuna salad. It is full of healthy fats and fibre and is nice and creamy. It gives great texture and works well with eggs and tuna.  You can use it for chicken or salmon salad as well.
You can use one whole egg and 5 or 6 egg whites when making your egg salad to cut down on the fat.  Tuna should be packed in water and look for the low sodium ones.  The less that is added to your food the better so that you can control how much fat, salt etc. goes into what you are making.
Add cut up celery, onion, pickles, a dash of mustard, cayanne pepper (one of my favourites) and whatever seasonings you like to kick up the flavor.