Two years on an open can may very well be the official time they want you to use it by but let me assure you it will last much longer than that if stored carefully. I have used Coleman fuel that was very old (8-10 years) with out any problems. I use Nalgene or MSR type fuel storage bottles so once I open a gallon it is stored in aftermarket fuel bottles and I have never had to dispose of any of my old fuel!!
I keep careful track of fuel age by marking the cans with the date they were bought and using the oldest fuel first. But that and good storage will make it last a very long time.