How much gas do most of you carry onto the trail if you're going out for the weekend?

Trying to figure out how many 20L(5gal) Jerry cans I need to aquire from work, and how much room to budget in the back of the 4Runner(2nd Gen).

 

I never need more than one for a weekend, but usually take two to be safe

 

18 gallons in my main tank and 16 in my aux. Unless I am driving ALL weekend, I don't use it all.