Do not be in the nether without an active fire-prot potion.
There really is no need, except the very first time when you grab a couple rods - for that, I suggest at least SOME fire-prot armour. But if you fall into the lakes, well... you're 95% screwed.
After your first time, spend like 10 mins with your brewing stands and make a chest-full. Keep that chest next to your portal, or - even better - make splashy potions, hopper it into a dispenser with a pressure plate.
With fire resist, the nether is a playground; safer that overworld.
For the tiny cost of the 8 minute potions, why would you not be fire resistant? That's just carelessness.
Keep a couple in your ender chest, along with obby and a lighter; with any decent kind of pick you can get anywhere in the world, 10k blocks in 5mins