Most things have an expiration date although most things aren't good one day and bad the next. How long have things gone past the expiration date and still been effective?

Depends on what it is and how long the expiration date was. If the expiration date was rather shorts (days, weeks), then I generally just toss them.

Cans good or sterile medical goods, which last for years before it hits it's expiration date. I have no problem using them weeks or a few months after expiration, as long as the packaging is intact.

Ofcorse always use your nose and eyes. Smells or looks funny, than it goes straight in to the dumpster. Do note, that things do deteriate with time. So with food it might be taste. Medical supplies; sticky things start to stick less (or won't unstick from eachother in the package) and elastic things start become less elastic, etc. Which could also happen even before the expiration date when stored in crazy temperatures. So don't go years over the expiration date and think everything still works like new.

Note there are 'use by' and 'best before' dates.
If it's significantly past the 'use by' date throw it.
'Best before' is not so important
qjs

Tetracyclines, I've read (https://en.wikipedia.org/wiki/Tetracycline_antibiotics), become poisonous past the expiration date. Don't take any chances with them. Other meds start to lose efficacy but are unlikely to harm you. In many cases the state of the packaging and the temperature of storage are far more important than the amount of time that's elapsed.

One otherwise potentially lifesaving medication that requires close attention to the expiration date is sublingual nitroglycerin tablets or sprays, because they rapidly lose their effectiveness thereafter, or if exposed to heat. Also, once the bottle is open, it is probably best to discard and replace it after six months, although some new research has questioned the latter recommendation.

Most medications, with some notable exceptions, just gradually lose their effectiveness over time.

If you take a lot of medications, there are online applications that allow you to list them all and check for any interactions between them.

If you get prescriptions from different doctors, make sure they each know what all of your doctors are prescribing for you, especially your primary care physician.

Pharmacists are a grossly underused medical resource, and they are usually quite happy to answer your questions and fully explain everything you need to know about how to safely use your medications.

Some medications need to be kept in their original container rather than in daily pill cases, especially if there is a desiccant in the bottle. When travelling, especially internationally or with controlled drugs, you should keep your medications in their original labeled bottle.

Right. My big FAK resides in my car's trunk. So I've switched to a foam insulated nylon kit bag, and I've placed most individual components in vacuum-sealed plastic to reduce deterioration due to air exposure. I also store the lithium batteries for the pulse oximeter and flashlight out of the devices and in vacuum bags. The heat still causes the rubber tubes and bladder in my sphygmomanometer to get a little gummy, though.