All depends on one, the size of the unit and it's thirst, 2, how many you use and 3, how much you run them. A 5 gallon can may be fine.
For me, I'm running 2 large Kubota's every day in the summer when farming and while both are pretty good on fuel, I may sill fill them (30 gallons each) multiple times a day so I need fuel in bulk. Consequently, a 5 gallon can is a no work here.
Both my fillers are fairly low (I don't much care for the middle of the hood fill on the smaller Kubota's), mine are beside the steps on one and next to the 3 point on the other.
I actually have a 100 gallon tank in the truck so if I'm out in a field and I need fuel, I call my wife on the fm transceiver and she brings the truck out and I fill in the field.
All in what you need and how much you use the equipment.