Camelbak hydration system. Angie (who is the greatest wife ever) got one for me for my birthday this year. It's something I've always wanted try but never felt like spending the money on for myself. For me, water bottles have always worked but the Camelbak seemed like a great idea. And for longer bike packing trips, this will allow me to have a couple water bottles packed away while having this accessible on my back.
I was surprised how quickly I forgot the pack was on my back. It's small enough (and well designed enough) that it didn't affect my riding at all. And I did stay hydrated much better than I normally do. I continued to grab a quick sip as I pedaled down straightaways or stopped momentarily to navigate. That was the biggest benefit to me. I'm terrible at keeping water going in. Perhaps the newness of this kept it in the front of my mind. But hopefully I'll do a little better when riding dirt.
I also liked that it allows a bit more storage. It's got a small pocket for keys and wallet and I used the bungee cords to strap in a rolled up rain jacket. It had space for what I needed without allowing me to be the guy that carries everyone else's stuff :)
This won't replace water bottles, though, by any means. For commutes and road rides, the water bottles are much simpler. But camping and mountain biking will certainly benefit from this piece of gear.
Get out there.