Ah, no. Please don't carry any extra gas. If you were to be rear ended or were to rear end someone else, that container of gas would (could rupture) and splash forward and ignite. Need I say more?
Another risk equation...for those who may want that extra measure of safety, I recommend these https://www.amazon.com/gp/product/B0002YW4US/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
