To start this one off... Just keep it smart and save people! Fuel is awesome to get your motorcycle running but you do NOT want to run away from your motorcycle because it is on fire.....
First of all... Can you transport extra fuel?
Yes, if you do it wisely. The Agreement on Dangerous Goods by Road (ADR) that all European nations abide by states that private individuals are exempt from its zillions of pages of requirements "provided that steps have been taken to avoid any leakage of contents in normal conditions of carriage." After that, all you need to do is adhere to the Road Vehicles (Construction and Use) Regulations, which essentially mandate that a load be secured to prevent it from falling off. Therefore, provided you have a suitable container and have strapped it on securely, you're good to go.
Is it dangerous to transport extra fuel?
YES, so be smart about it! On the other hand, it could also save your life...
Predictably, the majority of risks involve gasoline seeping out and setting you ablaze....
Your container's seal is leaking. This can occur due to user error, but it frequently happens because the fuel dissolves the lid seal because the container wasn't made to hold fuel.
During a crash, the container separates. Again, utilizing a Lucozade bottle as opposed to gasoline can greatly increase the likelihood of this happening. If you've put the container in your backpack, things could get even more dramatic. The fuel dissolving the container can also cause it to leak. It's obvious that this is the case because it is an improper fuel container. You lose control since the container isn't adequately secured, which is a nasty surprise for other riders...
So, how do you carry extra fuel?
Attach a five-liter gas container to the back with straps. The simplest alternative is acceptable in an emergency, but it can be challenging to secure them correctly. If you're worried about the seal, they're difficult to keep vertical because of the unusual shape and loose tie downs. It's a good long-term choice if you can fit one in your tailpack.
You can also use bottles of camping petrol. These can fit down the side of your panniers because of their varied compact sizes (such 0.5 or 1 litre). One litre should get you off a highway, but not necessarily to a gas station, if you ride carefully. You can travel at least 10-15 miles on one litre. It is wiser to put one in each pannier. You can clamp or zip tie your clothing to a frame spar if you don't want to store gasoline near to it.
Storage containers that stack. This is where things start to get serious; these bad boys are more of a world tour possibility than a necessity for a short trip. The extra fuel they provide per can ranges from 4 to 20 litres, and you can double them up for the whole apocalypse spec. They may be bolted on to pannier frames, rear racks, or engine bars. There a sxome very nice container & transport systems on the market, so think about that before you do something "creative".... for example check Overland Fuel out [Click]
You can also use larger main tanks and/or auxiliary tanks. Yet another thoughtful response. A tap is used to turn on the auxiliary tanks, which typically sit on the passenger seat and are plumbed into the main fuel line. Although some GS owners have installed the larger tank from the equivalent Adventure model, larger primary tanks are common among overlanders riding tiny trail bikes.
In the end you should decide what is best for you. The less you need to carry, the better. So be smart about and make sure you keep it save and simple!