I have a nice road bike and take long group rides.

My problem is that I have not place to stow cloths and the like.
When you start the ride it is normally colder and you might need a extra layer or rain jacket.

I was think about getting a handle bar bag https://www.performancebike.com/bikes...&top_category=

But have a few concerns:

1) Does it have a big aero impact?

2) Is it just to fred?

3) What other brand bag?

Please feel free to provide other suggestions.

Jersey pockets

From what I've heard it doesn't affect aerodynamics very much,and who cares about Fred.However fitting a handlebar bag on a bike that has brake lever shifters can be a hassle.The shifter cables come out the side and get in the way.There are adapters that you can use to reroute the cables so that you can mount a handlebar bag.
There are other options too,saddlebags such as Carradice bags can be mounted to almost any saddle(they do asy that you need saddlebag loops like those found on brooks saddles but that is not nessecary).They can be mounted to regular saddle rails if need be.
I would stay away from seat post mounted racks a bags though because they do effect handling,if thats even possible with your bike.

Baloney. My touring bike has a 40cm wide bar, Ultegra STI shifters and a handlebar bag that's more than twice as large as the one the OP wants to buy. No problems: I push the cables out of the way and the tips of the levers just clear the bag when shifting.

I have this and it doesn't get in the way of the cables.

I'm thinking you'd look fabulous with this one...

There's a local randonneur that uses the same bag. He's put a lot of miles on it.

For $20 it's worth a try.

I didn't look at the bag you were thinking about getting,I was thinking full size bag,but that looks good.
I say give it a try,a bag like that can't affect aerodynamics or look to strange.
Looks to me like that just makes scence particularly if like me you don't like putting things in your jersey pockets.

A stuff sack and a strap or bungee will suffice for a windbreaker.

I ordered the bag, for $20.00 it is worth a shot.

I think the hassle of folding and strapping is difficult and does not look good.

You can get mid-sized saddlebags that can carry sufficient for a day ride. Carradice make traditional ones and modern quick-release ones using the SQR system.
Bar bags are good for solo rides where you are navigating a complex road network, they are a handy platform for your map. There is some aero drag compared to a saddlebag but the ability to navigate on the fly really speeds up your average time.

What about a pack instead, especially if you don't care about the fred factor. plus when you stop somewhere you dont have to worry about someone stealing from it.

Whatever works. I've wrapped a light jacket around my top-tube a couple of times when I've been expecting rain. Looks kinda' dorky but it works for me.