If you buy conditioner at a drug store, you get a plastic bottle, mostly full of water. Just like bottled water, that's wasteful of energy shipping the water around, and wasteful of plastic. In addition, it usually has a bunch of possibly harmful chemicals in it. I figured that if I made my own conditioner, I could re-use a bottle hundreds of times, ship less weight around the country, and know what ingredients I am using. And at the same time, save money--my formula can make 16 oz. for only 12 cents!
If you want to check out the safety of the conditioner you are using, you can look it up at the Skin Deep
cosmetics safety database. You can also search for low-toxicity conditioners. When I tried to do that, I found stuff that looked really benign, but cost $20 a bottle, plus shipping, and I wouldn't be doing anything to avoid buying bottles and shipping water around the planet.
So I looked for conditioner or hair gel recipes on the web. There are some out there, but a lot of them use the same chemicals that I'd prefer to avoid. There was one that worked great -- boiling flax seeds in water to make an amazing gel
--but the result goes bad in less than a week and ends up smelling like rotten eggs. It's worth considering doing that and keeping it in the fridge to prevent spoilage, but I wanted to see if I could make something more convenient.
It turns out that this formula also has something of the same problem--it spoils eventually if it's not refrigerated--so unless you want to add preservatives, you need to make small batches, or keep most of it in the fridge. But it works well--as you see in the comments, some people swear by this formula.
Several comments also suggested aloe vera juice. You can buy that in a bottle or grow your own. That's also likely to have the problem of needing preservatives to last without refrigeration, but it seems to do a little better in my limited experimentation as far as keeping at room temperature.