I also worry about use by dates and have posted on here in the past about a few things I was unsure of. I'd say as long as it smells ok and not putrid and as long as you cook it to a specific internal temperature, it's fine. Red meat cooked to an internal temperature of 160f/71c and chicken cooked to 165c/74c kills bacteria. I always used my thermapen to check for those temps. And leftover food to be reheated should also reach 165f/74c.
What I generally do when I buy mince beef, sausages, chicken thighs or drumsticks is freeze them if I don't intend to cook them the same day or if I'm unsure if I might even cook them the same week. Particularly when I buy them at a reduced price if they're being sold on the actual use by date. As long as they're frozen before the use by date has passed, they'll keep for ages, but once you defrost them, then they must to be cooked the same day. I happily defrost sausages and mince in the microwave and 500g of minced beef only takes a few minutes. But I defrost chicken overnight in the fridge as my understanding is that it's safer.
One other thing. If you plan to freeze meat or chicken, prepare ahead by splitting them into the portion sizes you'll want for single meals before freezing, otherwise they'll be stuck together and you'll have to defrost the whole lot. It's pretty much impossible to pull apart the amount you want to cook once frozen without resorting to a hammer and chisel. With a pack of 8 sausages for example, I split into two lots of 4 and wrap each portion in clingfilm.