At gas pumps, Samsung pay will work most of the time, just have to do it right. Press "pay here credit" or whatever buttons you have to do to get the pump to say insert card. Activate samsung pay with your finger print, hold the top of the phone near the insertion slot, then insert and remove your driver's license with the mag strip DOWN (the gas pumps read mag straps on either side at the top of the slot). Inserting the license activates the card reader, which allows it to receive the information that samsung pay is telling it. As many people here have said they only carry a license and their phone, this should be beneficial. And as your doing it yourself without ra line of people watching, should be able to experiment and take your time to figure it out with out any stress.
If you find its not working or getting declined, simply as the cashier to press the "credit" button then try again. As for fiddling around and trying to find the sweet spot, just look at slot for the card sniper, look down the slot... you will see a shiny half moon thing in the slot. This is the reader. This is the sweet spot. This is where you should hold the phone, as this is the part that is looking for the signal from Samsung pay.
But the most important thing to remember.... this is NOT apple pay/android pay/NFC. This can't be disabled by the businesses, and it works where you can swipe a card. Chip card readers have no effect on it eithe.