I don't think many people are aware of options when it comes to being zero waste.
Cairo eats chop, so it's all fresh foods. I make sure to buy them unwrapped from the grocery store and from the wet market, and when I buy them, I put them into mesh reusable bags (unfortunately, we still have to get the sticker that says how much it weighed and how much it cost).
When I buy non-fresh foods, such as his dehydrated flowers and veggies, I buy those at an organic bulk food store and bring my own glass jars that used to be pasta jars.
I do bulk make his chop, which is a struggle for me in terms of waste. I am trying to slowly build up my Stasher bag collection (reusable silicon bags that can be frozen) (and I'm trying to buy secondhand). In the meantime, I wash and reuse the plastic ziplock bags until they start leaking (normally about 2-5 reuses).
However, I do small things like, when I strain the capsicums, I save the liquid and use it to make birdie bread.
Yes, Cairo doesn't eat all of his food, which actually works great for us. We put his leftover food into our vermicomposting bin, so the worms absolutely love all scraps of food from him. When I make his chop, I save the scraps (carrot peels, withered stalks, butternut squash skin, etc) and give to the worms.
In terms of his poop, we don't buy linings or anything like that - our neighbour gives us newspapers for free. (In Singapore, we don't really recycle - everything gets incinerated, so it's better to have a second use for something before it gets tossed.) My partner is hoping to compost the newspapers as well, but I've been asking to hold back on that (I know if you dry it properly it is safe to compost; however, I want us to get more confident with our composting and our vermicomposting first). Instead, I use the soiled newspapers to absorb any oils or wet meat-based food waste before we toss it out.
In terms of his poop outside the cage, he is potty trained, so he'll stick with one area that I can put newspapers underneath.
For overall cleaning, we have a Dyson, so I don't need to buy replacement vacuum cleaner bags - just pop open the bottom and dump it out. Even his feathers can be composted

but I don't particularly care to.
With his cage and toys, I buy F10 concentrate, then just top up with self-dilution and reuse the same spray bottle.
In terms of bigger picture, we're expanding our gardening to include more edible stuff for Cairo, so we don't need to buy as much (less importing from overseas). When we go to fly him outdoors, the only sitting space is at Starbucks, so we bring our reusable cups to order drinks there. I do try to buy plastic toys secondhand (I feel more comfortable soaking them in strong F10). We don't have a proper cage cover for him, but we use a secondhand IKEA blanket instead. We buy his treats (almonds) in bulk and easily store them in tiny glass jars I repurposed from being hotel jam jars.
We're trying in small ways and slowly trying to find new ways to improve.