I've got a friend who's a butcher and he would never chuck meat just cos it was a few days out of date. As everyone has said here, if it smells bad (and not just a bit funky because of the plastic) but REALLY bad, then chuck it. And just always cook food properly.
I remember watching a programme where this woman was going through her fridge saying "these yogurts, their use by date is day after tomorrow so I'll bin these and buy new ones today" An obscene amount of waste.
Quick question of my own though ... roasted chicken yesterday. Put leftovers in microwave to cool down before putting in fridge (keeps it away from cats). Totally forgot till this morning. Would you chuck it or do you reckon it'd be ok?