I save packaging from things I order for myself - boxes, padded envelopes, re-sealable bags, bubble wrap - and re-use them for Vinted/ebay sales, but I also have a set of plastic mailing bags which I use if I run out of recycled stuff or it's not the right size. Just google "plastic mailing bags" and get a set with a few different sizes.
The padded envelopes/bubble wrap bags are my favourites, but too expensive to be it worth buying new, so they always come from the recycling pile.
If it's a slightly nicer item - like a silk shirt, say - I wrap it in tissue paper, another bag (clean bag for life will do) and only then do I put it in the final packaging/plastic mailing bag. And I always tape it really, really well with duck tape; whatever the order is.
I've never sold a pair of shoes with the box - I don't think this is expected - but depending on the type of shoe, I might bubble wrap them or add some padding for extra protection.
That might be overkill, but a lot of my reviews mention good packaging so I think it's appreciated!
Good luck OP, it's actually really fun once you get going :)