UK households contribute about 70% of total food waste each year, and globally (if it were a country) food waste would be the third highest emitter of greenhouse gases. Clearly the best way to avoid food waste is to only buy what you need, and don't bulk buy fresh products that you can't use before they go off. We all know this is easier said than done. (Be honest: who else buys something planning to make a specific dish but then discover you're missing a vital ingredient so you forget about the delicious new thing and go with the old faithful again, only to find some sad and soggy celery at the back of the fridge a week later?)
It's much easier to keep on top of food wastage if you can create meals using what's in the fridge and cupboard. Although many long-life products (tinned veg and fruit for instance) are higher in salt and sugar (they are used in preserving/curing processes), it's easy enough to check the ingredients list, and keeping a good stock of cupboard basics (including rice, pasta, dried pulses) means that it is relatively easy to bulk up fresh produce as needed. This means you can buy less and do more. If you do find yourself with a glut of something look for a recipe you can batch cook and freeze rather than throwing unused food away. This may become more relevant over the coming months as many more people are now 'growing their own', even those without gardens. On which point: if you do have a garden, you should really have a compost heap.
The pandemic has had a huge impact on what we now call ‘normal’. Including changing how and what we eat.
The restrictions on shopping have meant that more people are planning ahead and buying in bulk either to limit time in the supermarket or to save money. Bulk buying isn't necessarily the best practice as it can mean there is not enough for everyone. I'm not going to mention loo rolls but many new sourdough bakers found that flour was hard to find last summer. Partly this was due to a poor wheat harvest and partly the flour industry wasn't prepared for the change in the supply chain which created a packaging problem rather than a production issue. Bulk buying didn't help. But we have adapted and learned, and, despite all the problems associated with working and schooling from home, many have discovered they have more time for home cooking, with potential dietary improvements as a result, as well as reduced home waste. And it's not just physical health, some also see benefits to their mental wellbeing, either through learning new practical skills, or perhaps just through the meditative practice of kneading. Incidentally, kneading is also a pretty good physical workout if you need to release some aggression.
Finally, as always, everything in moderation, keep perspective, and don't beat yourself up for chucking away that soggy celery. There's always next week.