Fuel becomes essential at higher levels, you need it to upgrade and craft weapons/gears. You can usually find fuel in stores, streets, and supermarkets, also cleaning up your base is also an option.
Junks can be recycled for craft able parts, wood, steel, and cloth. Cloth is the most valuable of the three because of it's rarity, which is only findable in fabric based junks, which is mostly found in Residential areas.
A leader specializes in anything, useful at healing in the beginning. I suggest you to balance out every skill for leaders.
A Fighter specializes in assault rifles,SMGs, and close ranged combat. Useful at protecting an area when someone is trying to scavenge out an area.
A Engineer Specialize in anything with Improvised on it.
A Recon specializes in Long rifles and sniper rifles. And are really agile.
A scavenger specializes in pistols and such, can also scavenge quicker than any other Class, they also hack luck, which lets you have much better findings then any other class, EG: Leader salvages 2 water bottles, A scavenger can salvage, 4 water bottles.
A Medic can heal others, but is really the most disposable class since a leader can also heal.
Hope this helps.
