I used to use hydration tablets, then I had a proper look at what was actually in them after noticing they didn’t do a lot for my stomach – they pretty much all use artificial sweeteners like Sorbitol, sucralose, aspartame etc, some of which are actually laxatives. Other stuff too, they are all packed with chemicals, ditto gels. This seems like a bad idea to me and my guts.
There’s a proper shortage of anything similar using all natural ingredients, closest I could find was the Skratch Labs stuff, which works for me on one-off, big ride stuff, but is expensive and relatively hard to source.
Other than that, I use a mix of fruit juice and water maybe with a pinch of salt thrown in if it’s warm and I’m planning on serious sweating. Eat bananas and food. Team Sky used to use dilute pineapple juice partly because it’s more interesting to drink than plain water, s it get drunk more easily.