Why? Why not give those things directly to the foodbanks? Better still, give them the cash and let them use their considerable heft to achieve better economy and buy more with it? Why is it better for somebody else to have to load and move all this stuff? It won't be given to foodbanks, it will go to landfill.
Why must 'things' be left? Unwrapped flowers, is one thing although in that quantity they just look a pulpy mess very quickly. But, public does what public wants. There is though some wilful ignorance about waste disposal and what that looks like in reality. Paying council tax really doesn't cut it.
It's not grief though, it is wanting 'to be part of history'. Leaving sandwiches, flowers and queueing for 10 hours does not make you part of history. You're already there, we all are, we are living in this time.
As for 'paying respects', what does that even mean? The flower throwers (onto the cortege) are not paying respects, they are being attention-seeking, that's an easy one. Walking past a coffin, is no more paying respect than not doing that. My definition of paying respects is doing things for the bereaved family, not wanting to encroach on their grief and try to appropriate it.
Blanket disclaimer: People can do what they want, there's no law against it.