When you finish the third Act, go to the Hotel and down the hallways until you get to the lounge with the table and chairs. There will be about ten alcohol bottles on the bar there that you can take. The great thing is these bottles will respawn once you leave the Hotel and re-enter it!

Grab as many of the bottles as you want and then go to Harland and trade them for Molotov cocktails. You can repeat this as many times as you want and it's a great way to get free Molotov cocktails!