I just kid up ordinary salt and low-sodium salt to give me sodium and potassium. I've tried making fancier versions, with Vit C, acetyl l-carnitine, d-ribose and magnesium and such, buy it doesn't dissolve in cold water well, leaves residue, tastes odd, and if you use d-ribose and a water bottle, causes a mould problem. I don't get on with d-ribose anyway.
Bear in mind that original rehydration drinks were for people with diarrhoea, who need the extra sugar. Then that became the norm for electrolyte drinks, and practically everything commercial has sugar in it by the bucketload, so that's what was being sold. Most people do not need the extra sugar. You need to be seriously low on calories, e.g. due to severe diarrhoea, before you are short of the calories the sugar in an electrolyte drink. Plus people with ME tend to react badly to sugar. Nuun, which just has a bit of sweetener and a nice balance of electrolytes, is a very popular electrolyte drink over on the DINET board for people with POTS. I keep some tubes of it around, in my handbag and so forth, so I can have it when I'm out and it's not convenient to put salt in a water bottle. The cola-flavoured one with a small dose of caffeine in it can be quite useful for attacks of breathlessness. The rest of the time, it's salt and reduced sodium salt in water.
People with ME often find that their weight is a problem one way or the other. I tend to run overweight, so I don't need extra calories. If you tend to run underweight, or you sometimes need a drink with calories due to skipping a meal, look into what drinks naturally have a good balance of electrolytes. Tomato juice is one, although it's quite acidic, which is a problem for some people. Milk is another, as I discovered when my partner commented that it really perks him up when he's tired and headachy. (So is soya milk, which is useful for me as I can't drink dairy.) I wonder if there's a list somewhere of drinks that have a nice electrolyte balance? For all I know there could be some high-water-content foods as well.
Oh, and as for the other supps, I take them in tablet/capsule form, which means I know exactly how much I'm getting per day, rather than just refilling my water bottle with a half-teaspoon scoop of mixture every time I refill it with water and then drinking varying amounts of that. It's much easier to tweak what I'm taking (magnesium in malate form doesn't come powdered that I've noticed) and how much of it, and it's just easier all round. I remember that despite having an anti-dessicant pouch in the Vitamin C powder, it still dried out and got stuck together, and you only need a small amount of that at once. Oh, and never EVER try to eat magnesium powder from the spoon if you're in a hurry. You end up with a chemically burned oesophagus and spending a week on medicine that tastes like a combination of aniseed, bicarbonate of soda, and soap.
So when I don't drink sodas it's not that I'm showing restraint or trying to be healthy. I just hate the taste of carbonated drinks other than the occasional ginger ale.