Some airlines and other travel partners still have COVID-related free cancellation/change policies (though they are usually a lot more restrictive than they were a few months ago). There are also travel insurance policies which deal with this (but read the fine print). As for having to postpone appointments... that's just part of life, this happened for many other reasons before COVID, this will continue to happen.

Could you clarify whether by "test failure" you are asking about (a) the test not coming back in time, (b) the test being inconclusive, (c) the test showing a false positive, (d) the test showing a true positive? Because the risks and mitigations are pretty different for all four.

One thing to note is that many airlines, hotels, car rental companies, etc, have relaxed their cancellation policies in the past two years, so it is much easier to get a refund or at least credit toward future travel. Thus most people would not be out "thousands of dollars" if they had to cancel. Likewise, people in general have become a lot more understanding when others cancel in-person activities unexpectedly for COVID-related reasons; if your friends and business partners are not understanding in that regard, then you should maybe look for new ones.

I don't have a full answer for you, but if you look at my most recent questions you'll see that some of us just sort of went for it assuming everything would be fine and are now dealing with the fallout of that naivete...

It depends where you're travelling to and from. A month ago I flew between Spain and England and didn't have to show PCR or LFT results - I only had to upload the QR code on my vaccination certificate to the different systems operated by both countries and everything was fine.

I second @gerrit's comment. Most sane people would consider it far more unacceptable to risk infecting business partners with COVID (substitute whatever nasty and potentially lethal disease you want there, this would not be a point of contention if it were something like tuberculosis or influenza being discussed) than to not be able to make a previously scheduled appointment. And if said business partners can’t accept that, then I would seriously question what other potentially serious risks they are taking that might affect your business ventures with them.

I am travelling internationally almost every month, and I never tested positive for COVID prior or during a trip. I suppose it works the same way as with any other illness. If you become sick, you might want to change your travel plans and recover at home.

Even if you're recovered from covid you can still test positive on PCR for weeks or even months afterwards. If you're intending to go somewhere with PCR requirements there is no solution - either you make sure you're PCR negative ahead of time and keep yourself quarantined until your trip OR you wait for restrictions in your intended destination country to change. The risk cannot be easily managed.

How are people coping? I am coping by not traveling to any place that has these annoying requirements. Any country that wants tourists has removed that requirement long ago.

@gerrit I don't read that the OP is suggesting that they give up testing and travel with Covid, they're simply asking how people who do travel in the context of possible Covid and testing manage the risk around bookings and so on

@J... It's possible to enter some countries with a COVID recovery certificate.

@Jake And some require a negative PCR. OP is asking about the latter.

@J... OP was, but it's still a valid point. In most cases where a PCR test would be normally required, a COVID recovery certificate is also accepted, because as pointed our earlier, you can still test positive well after recovery.

@Auspex I seemed to recall that yesterday it was known this was not an option for OP's intended destination but either i'm losing my mind or those comments are gone now.

A hypertechnical comment: the title's "24-hours" is not the same as the quoted language's "no earlier than the day before departure" wording.

This isn't really much different than having to deal with any illness you might get that could disrupt travel plans. If you became sick with the flu right before traveling, you'd also have to cancel your plans, reschedule appointments, and eat certain costs (assuming you're not a complete asshole that would risk infecting dozens of people on a crowded airplane). The only difference is that for COVID they want evidence that you're not sick.

@gerrit in the UK the official government guidance is now to pretty much go to work as normal even if you have COVID. The definition of "endemic" is indeed that its no longer a big deal if you test positive (though you wouldn't be getting tested in the first place). The new expectation is that people wear a mask if they're actively symptomatic, not that they stay home.

overall you can reasonably expect 99% of your friends/business partners to have COVID antibodies now (see UK antibody survey results) so its like a cold to them

by the end of the year this should become the official government guidance for all nations other than China, given the latest trends

you get covid, you cough for a couple of days, you move on.