Anyways in regards to the topic. 5:3 has clearly mentioned that what we can't eat:
"5:3 Forbidden to you is that which is already dead, and the blood, and the meat of pig, and what was sacrificed to other than God, and that which has been strangled, and that which has been beaten to death, and that which has fallen from a height, and that which has been gored, and that which the wild animals have eaten from except what you managed to rescue, and what has been slaughtered on alters, and what you divide by the arrows of chance. This is all vile. Today the rejecters have given up from your system, so do not fear them, but fear Me. Today I have perfected your system for you, and completed My blessings upon you, and I have accepted submission as the system for you. So, whoever is forced by severe hunger and not seeking sin, then God is Forgiving, Merciful."
Some like to add more things such methods of killing or things you can't eat but they are wrong as verse 6:45 points out:
"Say: "I do not find in what is inspired to me forbidden except that it be already dead, or blood, or the meat of pig, for it is foul; or what is corruptly dedicated to other than God." Whoever is forced without seeking disobedience or transgression, then your Lord is Forgiving, Merciful." (6:145)
Thus any additional rules some of these traditionalists like to add like lobster, crab, shot with a gun or arrow, putting to sleeping, electricution are not mentioned therefore the meat you buy in the west is not forbidden at all. Course one thing I say to watch out for is veil as I heard a story from my friend (not sure if its true though) that they make veil die of itself by keeping it in a cage. Course that needs more research if true or not.
Course then you got those who say 6:121 states you can't eat meat that doesn't have the name of God on it at slaughter. That is also false. 6:121 mentions nothing of slaughter nor meat. It simply states not to eat something(any type of food) which doesn't have Gods named mentioned it. some will argue there that it indeed requires it at slaughter otherwise its forbidden but as 6:145 mentions it, there are no additional rueles other than what is mentioned. The closest thing would be the opposite that is mentioned which states not to eat that which the name of God has been invoked on but never states if the name is not mentioned on that its not okay. Thus simply stating "Bismillah" before eating it covers 6:121.
Therefore eating a Big Mac, or KFC or a meaty sub at subway is in no ways forbidden.
The whoke "halal" market is in my opinion a scam. Coming out of hadiths and many other things and likely made up for the purpose of scamming muslims to buy their expensive meat. Hell they've even to lengths of trying to state Christian and Jewish meat is forbidden when the Quran has specifically mentioned them as lawful.
Funny enough we have hadiths where the Prophet was asked if they can eat a meat they were unsure was slaughtered with the name of God on it and he simply said to say Bismillah and eat it.