Taking extra fuel with you

[duive01]

I want to take extra fuel with me on my travels.
I'm sure there is written a thing or two about this subject but I couldn't find the answers I was looking for.

I have a jerrycan and used it some time ago in my car. But I noticed the jerrycan was leaking a bit at the cap. Are all jerrycans leaking or have I done too much fuel in it? Can you fill a 5l jerrycan with 5l or is it better to do 4l in it (or fill up a 10l can with 5l petrol)? Or was it just a bad sale? As you can understand I'm afraid to buy another leaky messy jerrycan and smell of petrol my whole trip.
What are your experiences?

I also heard that in France it's forbidden to drive with a full jerrycan! Is that true? Is a half full jerrycan not forbidden? Are there more countries that have these restrictions?

And what about fuel bottles like they use for cooking? I could take 2 or 3 bottles of 2l filled up to about 1.7l. That is also 5l of fuel.
Does anybody has experience with fuel bottles? I hear they are difficult to fill because of the pressure behind the fuel while filling up.

I'm really looking forward to hear about your experiences.