Magnesium glycinate pills at night are great for replenishing electrolytes and help with sleep and general mood/calmness. You can probably get enough sodium from your food and increase your consumption of potassium-rich foods during your eating window, but you can also add No Salt and table salt to a glass of water, (I add lemon juice as well.)
I personally use Keto Chow Electrolyte Drops, I first heard about them through Megan Ramos from The Fasting Method. They are flavorless and super concentrated, I just put a squeeze into each beverage I consume on a fasting day and don’t notice it.