How much does your generator use per day and how long until you can reasonably expect to be able to resupply? That's about how much fuel you need.

I usually keep 20 gallons of alcohol free gas in nato cans treated with stabil. 5 gallons of diesel in a nato can with some anti-algae treatment, it might not need it in the can but I need it when it goes in the lawnmower. With the humidity in Florida the air has algea growing in it. Also keep a gallon or two of the premix cans of shelf stable fuel for the chainsaws. It has a long shelf life and the engines run well on it.

The generator uses 5 gallons a day so that gives me 4 days of run time before I need to buy more or drain a vehicle. The generator gets serviced once a year, oil change and fresh fuel. It also gets started regularly during the year. The fuel rotation is once a year and most of it will go in the truck. The fuel cans and the genny all get tagged with the purchase date so I can remember when it was done.

Also, if you have a chainsaw whether it's gas or electric (I have both) have spare chains and a bar with it. If you hit an embedded object in a tree or it shifts while cutting and pinches the bar you can continue cutting with spare parts. This seems to be more of an oversight with electric chainsaw owners. I guess since they don't have to deal with anything other than spare batteries, they don't see the need for any spares.