I always have a backpack so I've never been short on tools. Get a small fanny pack/belt pouch, or saddle bag. Lot's of cycling specific companeis make them. Look for the ones that cater ot the urban rider. Buy one large enough to fit more than you think you need because sometimes you'll probably want to carry more things.

One thing I learned, get a multi-tool if possible. I opted to buy full tools, and didn't use them enough to justify their purchase. Multi-tool is perfect (quality one). The only real wrench you should have is the 15mm one for your axle nuts. Everything else you'll be adjusting or using so sparingly that a dinky multi tool version will be fine. Tools are heavy, bulky, and really really annoying to carry around and move out of the way when you're digging into your bike pouch. If you live close enough to a bike shop, a patch kit is just fine.
The less you carry the better.

Carry enough nutrition bars to substitute for a full meal if you're going anywhere sorta far.
I'm an adventure rider more so than one of these fast race dudes, and most riders probably fall into my category than not, so that's what worked for me.
My hydration always went into my backpack, but one thing I can say is that camel-baks are terrible. They are one of those items that sound like a good idea until you try one and it just becomes an extra part of your routine and you eventually stop using it because it's annoying. They might work for you, but I have a feeling that most poeple that use things liek that have a very specialized reason for doing so and they don't do it often.

If you're not a race dude and you are an adventure rider, be minimal and utilitarian.