If they aren't contaminated with norovirus, or e-coli, or whatever from some outside source, they aren't going to go bad from sitting out any length of time - either it was contaminated when you bought it, in which case it will make you sick whether it is kept refrigerated, or eaten as soon as you bring it home, or it isn't, in which case you can leave it out till it wilt and it won't make you sick.
This seems wrong, but I'm willing to be educated on it.
My understanding of food poisoning is that evil germs produce toxins that make you sick. When you refrigerate something, you slow evil germ reproduction, and the germs or their toxins remain at small enough amounts that our badass healthy bodies can deal with them. When you give them an environment they love, like say humid and about 50 celsius, they will reproduce faster, and make more evil germ poo that makes you sick.
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No. E-coli (esentially it comes from...you know: poo) has to be
in the produce. Keep it any lenght you wish in room-temp: if it wasn't there it won't grow - though the produce will rot or mould. Though, no salad or meat or cheese is germ-free and those (natural and nice) germs will, sooner or later ruin the food and cause you to get sick. The fridge will slow germ production, but not eliminate it (so you can easily get e-coli from refridgerated goods).
The problem, of course, is that greens (out under open air with birds, bugs etc) generally have a decent chanse of being infected with not-so-nice germs that'll make you ill unless you wash them.
That said, where I live we pack (all and sundry) our lunch daily and keep it in room-temp for up to 8 hours. No government advice on not to do it, and I've never heard of food-poisoning due to it.
