Here's what I go by based on personal preference and articles I've read or watched on TV news programs in the past. I'm too lazy right now to verify the information so obviously don't take it as gospel. And I'm guessing different products and places have their own quirks.

To the original question, no, I don't "ignore" the expiry dates but will use it for guidance.

Best before dates usually don't necessarily mean something is not safe to eat but describes when the quality of a product will have degraded past a specific point. I watched a news segment where people were complaining they bought meat (beef?) on sale from a grocery store that was beyond the best before date. The reporter, during his investigation, ascertained that the meat was still safe to eat but the publicity caused the grocery store to refund people's money.

I've also read or heard somewhere that all food products have to have an expiry date even if they will stay safe to eat a long time. But I've found some products that I couldn't find an expiry date so I'm not sure if this is a fact or not.

If you think about it, whether or not something is safe to eat is probably based on the amount of bacteria that's been able to grow on/in the food. (How cold do you keep your fridge?) So, depending on the food product, I'll may throw the product out when it reaches its best before date or keep it. I'll usually throw out dairy products like milk, mayonnaise, egg based products, etc. Meats are iffy. I'll usually keep dry goods like powdered mashed potatoes (great to thicken cream soups), pastas, etc. In the end, if I'm unsure, it'll go in the trash because I'd rather toss a $1 item of food than risk sitting on the potty all night.

As for drugs, I watched a 20/20 segment which said that the best before dates on the packages were based on the package not being opened and once opened, the drug may actually lose its effectiveness earlier than the date on the label. Another point I remember from the segment was that although it wouldn't necessarily be unsafe to consume the drug itself, if you are depending on a drug to keep you healthy/alive and the drug has expired and lost most of it's effectiveness, that in itself is "unsafe".
I've sent a note to my wife's pharmacist friend to get a "professional" answer.

Personally, I'll use Excedrin, Tylenol, etc past their dates but prescription drugs usually go in the trash.