Please forgive me if this is common knowledge and mass-employed, but I've not run across it.
Mayo is a wonderful thing, especially helpful on a low carb diet. Man, how can you choke down can after can of tuna without it? But commercial mayo is not as healthful (or tasty) as it could be. Mayo is also incredibly easy to make and incredibly easy to make healthful and delicious.
Crack an egg into a blender (you need a real egg for the lecithin, although you could probably find an alternative with a little work), add a cup of whatever oil you like (depending on your tastes you can go with vegatable, olive, nut . . . or my favorite, flax . . . hell, throw in some Sesathin if you want) and blend. Walk away, contemplate something deep, come back and scrape the mayo into a vessel. It should be good in the fridge for at least a week, probably two. There's no preservatives, so don't make it if you're not going to eat it.
Add anything you think would be good to the blend. Garlic is a common addition. A bit of salt is also suggested. You can customize it with seasonings that you like or that you think will go well with what you're planning to eat that week. I find that dill is great with fish and that rosemary is great with chicken; hot pepper, of course, always adds a little bump.