If you are not worried about your Dog Tag Level, then here is an easy way to quickly gather supplies.
Recon different islands to find some that have Oil Platforms located far away from the islands. If they are unguarded, simply deploy one or two boats to attack them. Gunboats and Heavy Gunboats are best because they will attack whatever is closest. If the island has 100,000+ supplies you can usually make 30,000 to 45,000 in one attack. You get the supplies whether or not you earn a star.